A question regarding the Epic Boon Feats

Quote from SmiteMakesRight_3_5 >>

That is RAW and you are giving up quite a bit to do. You wind up with the same number of feats, but one might be stronger than one of the rest of your party. However, your class features will be weaker to accommodate it.  If your sole goal is to get 2 epic boons, it is generally more advantageous to split 16/4. If for example, that is 16 levels of Wizard, you are not getting Signature Spell, Spell Mastery, 9th level spells, one less each of 5th, 6th, and 7th level spells, and you are preparing 4 less spells per day. You can mitigate the spell slot loss if you multiclassed into another spellcasting class. In return, you are getting the early benefits of another class, plus one feat is upgraded to an Epic Boon.

In essence, the Epic Boon becomes a sort of multiclass cap stone ability.

What exactly are you concerned with a level 20 character pulling off?

 Exactly, the point that should be made. This is a RAW interaction and deviating from RAW should only be done with great care and forethought. Reflexively denying a player this interaction only makes your game more complicated and difficult to balance doesn't it consider what those players are giving up for those 2 epic boons. Every classes is delaying their feat progression to do this. Until level 20 a player doing this will basically have 1 less feat than other players. That's a huge opportunity cost for the vast majority of play.

Any full caster is giving up preparing 9th level spells, their higher level class features including their capstone, and probably spell slots progression for 2 epic boon feats. What are they really gaining in exchange? A extra +1 in an attribute so you can have 22 in your spellcasting attribute and the features of 1 epic boon that you wouldn't otherwise get along with the lower level features of another class. I'm not sure that's worth what you're giving up especially some of the best 9th level spells like wish, shape change, true polymorph, prismatic wall, or time stop.

Even with martials and half casters I don't see it being objectively better in most cases. They also give up capstones which are pretty significant. Giving up your 4th attack as a fighter is a huge downgrade in DPR and not really worth it unless you already have a multiclass build set up. I definitely wouldn't do this with a monk or barbarian unless I had already decided to multiclass as well; their capstones are too powerful. I'd probably do it with a rogue or ranger though, especially a beast master ranger. You'd get the shared spells then go druid or cleric 4 levels and come back to ranger. 

TLDR: denying this RAW interaction punishes players for planning out their progression and making early sacrifices for later gains. That's not good dming, players should be rewarded for their character's sacrifices not punished.

While mechanically I know you can only get these if you get a feat at level 19 or 20 (or more than one depending on how you split up a multiclass), to me these feel more like rewards you should be giving your players for getting that far instead of something that can either be stacked or missed out entirely on. They add so much to the pinnacle of a character and unless you're playing in a level 20 oneshot, you're probably going to have a very good idea of what boon will fit that character thematically, influenced by the course of the game.

Honestly, I would just recommend giving players an epic boon feat at level 19, with the caveat that they can't have more than that one.

Quote from EurobeatJester >>

While mechanically I know you can only get these if you get a feat at level 19 or 20 (or more than one depending on how you split up a multiclass), to me these feel more like rewards you should be giving your players for getting that far instead of something that can either be stacked or missed out entirely on. They add so much to the pinnacle of a character and unless you're playing in a level 20 oneshot, you're probably going to have a very good idea of what boon will fit that character thematically, influenced by the course of the game.

Honestly, I would just recommend giving players an epic boon feat at level 19, with the caveat that they can't have more than that one.

If you want to make that house rule, that's fine but the PHB explicitly tells you how to get multiple Epic Boons even without multiclassing.