An Ioun stone is named after Ioun, a god of knowledge and prophecy revered on some worlds. Many types of Ioun stone exist, each type a distinct combination of shape and color.
When you use an action to toss one of these stones into the air, the stone orbits your head at a distance of 1d3 feet and confers a benefit to you. Thereafter, another creature must use an action to grasp or net the stone to separate it from you, either by making a successful attack roll against AC 24 or a successful DC 24 Dexterity (Acrobatics) check. You can use an action to seize and stow the stone, ending its effect.
A stone has AC 24, 10 hit points, and resistance to all damage. It is considered to be an object that is being worn while it orbits your head.
Strength. Your Strength score increases by 2, to a maximum of 20, while this pale blue rhomboid orbits your head.
Notes: Bonus: Strength Score, Buff
Ioun stones are some of the worst, most obsolete items in the game. The only one that's remotely good or unique is the stone of mastery, and even that isn't worth the legendary tier.
Now this, THIS STUPID ITEM, takes the cake for the worst non-cursed magic item in the game.
In fact, just to really, really underline your point, Belt of Dwarvenkind is a rare item. Meaning all of this:
+2 con
+resistance to poison
+Darkvision
+Language
+Advantage in charisma checks with dwarves
Is apparently worse than +2 strenght on the condition you've set up an effect that can be taken from you by anything that succeeds on an AC 24 attack.
I mean, magic items are relative. It really depends on what your dm is handing out. This is definitely not an artifact, but it's still a +1 to your Strength modifier. That's a pretty rare thing in dnd.
Its not worse its just not as rare.