There's no assumption, it's just a description of how the class works.
Except it's not how the class actually works. It's just your assumptive complaint about how the class works. And I pointed out why those Assumptions are faulty as well. Which those reasons are basis on the actual class and the things that it can do that you've ignored to reach that assumptive conclusion.
My personal opinion and it maybe more of a compromise than actually following RAW, since it isn't the clearest here, is that the Armor remains magic and can't be infused while the other pieces are open to receiving infusions. So to me this means that the Chest piece (as it is the one labeled Armor) couldn't be infused as it has a magical ability and would be considered a magic item. The other pieces though are no longer considered Armor for the sake of this ability, and so while they are part of the magical armor, the Armorer's ability separates them into separate items no longer classified as armor so are not magical items and can be infused.
Until we get clarification from WotC though, this in the end would most likely just end up being the DM's choice on what he allows you to do.
This is how I DM it. The RAW is obviously unclear (given the amount of disagreement) so until there is a clarification this is how I will DM it - since the chest piece seems to be the section that represents the magical armour itself it seems perfectly fair to me.
If a magic weapon cant be infused is the absolute rule then warlocks are in violation
Pact of the Blade
You can use your action to create a pact weapon in your empty hand. You can choose the form that this melee weapon takes each time you create it. You are proficient with it while you wield it. This weapon counts as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.
Your pact weapon disappears if it is more than 5 feet away from you for 1 minute or more. It also disappears if you use this feature again, if you dismiss the weapon (no action required), or if you die.
You can transform one magic weapon into your pact weapon by performing a special ritual while you hold the weapon. You perform the ritual over the course of 1 hour, which can be done during a short rest.
so if warlock can utilize its magical weapon pact blade then artificer can arcane armor magic armor.
and there is another issue druids wildshape can merge with magic armor, it doesnt need to fall off, in fact if warforged or armorer it cant fall off, its bonded to you wildshape literally cant force your armor off you.
whether warforged, armorer or wildshape your bonded to the armor even in anti-magic field, and it means the a warforged armorer wildshaped still retains all its infusions and can still cast magic thru it and all your infused gear as a artificer even thru dispel and anti-magic field.
a artificers infusion remain in a item indefinitely so a common magic tattoo replicated item infusion never is consumed it remains indefinitely on your skin, Till you die infuse over it past maxed infusions or forget the artificer infusion.
wait if you a astral spectral arms monk armorer when your astral spectral arms end DO THEY REGROW AS PROSTHETIC ARMS permanently as you use them as limbs and your armor knows you use them as limbs so raw yes? Thats a four armed monk now with permanent astral spectral arms and 4 thunder gauntlets wait thats really cool. Is there a limit to the astral spectral arms? for 3 bonus actions in 3 turns can i summon 6 arms?
False Equivalence argument.
They are two different classes using two different Class Feature's with two different sets of restrictions. The Warlock ability is not in any way an Artificer Infusion or the same thing as far as the game rules are concerned. They work by their own rules in two seperate cases.
The Warforged issue is a third Seperate thing and is still not a matter of Infusions. Nor are Infusions even close to the proper comparison for the sake of Artificers. It would actually be the Armorer's 3rd level ability which does in fact allow Magical Armor to be used. So your making an incorrect assumption on two levels by making this comparison. Nor does it allow your wild shapes to actually wear armor. Wearing Armor is a general rule, Wild shaping is a specific rule that would over-ride it. Being made a part of your body does not somehow magically stop the wildshape rule from applying. it actually makes it even more applicable and would Disappear into your new form and be unusable in the same way that your eyes would be if you assumed a form with no eyes.
Your Also completely incorrect about how they would work in an anti-magic field. All those abilities for using it as a tool as part of their casting would be suppressed and not work while within an Anti-magic zone, and on top of that even if it did work the magic itself would still not work. So your doubly stopped from casting magic as an Armorer artificer in this particular fashion inside of an anti-magic zone.
Your Also incorrect about things being completely indefinite. the Rules on Infusions give several ways that infusions can stop being infusions. A Magical Tattoo would not magically allow you to over rule your maximum number of infusions. And it would not keep a Tattoo that says it gets consumed from being Consumed. That is a part of the item and would function in that way regardless of the fact of whether it came about through an infusion or from simply being a magic item from some other source. it would end being an infusion and even a magic item when that specific magic items says that it would in either case.
Your Also incorrect about the Astral Arms thing because they are not and never will be physical parts of your body. Or even connected to your physical body. They are completely and entirely a supernatural ability given to the Monk through a class feature and function purely by their own rules. They do not magically allow a cross class artificer armorer and astral monk to permanently grow new arms, or change them to be replacable by prosthetic limbs because they are never actually limbs. They are only a feature that can be used in a vague aproximation of limbs at best. And in limited capacity at that.
There's no assumption, it's just a description of how the class works.
Except it's not how the class actually works. It's just your assumptive complaint about how the class works. And I pointed out why those Assumptions are faulty as well. Which those reasons are basis on the actual class and the things that it can do that you've ignored to reach that assumptive conclusion.
This is how I DM it. The RAW is obviously unclear (given the amount of disagreement) so until there is a clarification this is how I will DM it - since the chest piece seems to be the section that represents the magical armour itself it seems perfectly fair to me.
Chilling kinda vibe.
That is ultimately what i went with
False Equivalence argument.
They are two different classes using two different Class Feature's with two different sets of restrictions. The Warlock ability is not in any way an Artificer Infusion or the same thing as far as the game rules are concerned. They work by their own rules in two seperate cases.
The Warforged issue is a third Seperate thing and is still not a matter of Infusions. Nor are Infusions even close to the proper comparison for the sake of Artificers. It would actually be the Armorer's 3rd level ability which does in fact allow Magical Armor to be used. So your making an incorrect assumption on two levels by making this comparison. Nor does it allow your wild shapes to actually wear armor. Wearing Armor is a general rule, Wild shaping is a specific rule that would over-ride it. Being made a part of your body does not somehow magically stop the wildshape rule from applying. it actually makes it even more applicable and would Disappear into your new form and be unusable in the same way that your eyes would be if you assumed a form with no eyes.
Your Also completely incorrect about how they would work in an anti-magic field. All those abilities for using it as a tool as part of their casting would be suppressed and not work while within an Anti-magic zone, and on top of that even if it did work the magic itself would still not work. So your doubly stopped from casting magic as an Armorer artificer in this particular fashion inside of an anti-magic zone.
Your Also incorrect about things being completely indefinite. the Rules on Infusions give several ways that infusions can stop being infusions. A Magical Tattoo would not magically allow you to over rule your maximum number of infusions. And it would not keep a Tattoo that says it gets consumed from being Consumed. That is a part of the item and would function in that way regardless of the fact of whether it came about through an infusion or from simply being a magic item from some other source. it would end being an infusion and even a magic item when that specific magic items says that it would in either case.
Your Also incorrect about the Astral Arms thing because they are not and never will be physical parts of your body. Or even connected to your physical body. They are completely and entirely a supernatural ability given to the Monk through a class feature and function purely by their own rules. They do not magically allow a cross class artificer armorer and astral monk to permanently grow new arms, or change them to be replacable by prosthetic limbs because they are never actually limbs. They are only a feature that can be used in a vague aproximation of limbs at best. And in limited capacity at that.