Rod of the pact keeper, staff of woodlands, talisman of pure good/ultimate evil, and robe of the archmagi also do this. Now the disgustingly broken part unlike magic weapons all of this stacks if you can can attune 3 of them they would all work together for every spell.
For instance Robe of the Archmagi can be worn by anyone with a single level in sorcerer, warlock, or wizard. Wand of the warmage actually works for any spellcaster (including paladins and druids for example) and goes to +3, and rod of the pact keeper works for anyone with a single level in warlock also going to +3.
I am not saying every warlock is going to get all three of those items at their highest rarity and use all three of their attunement slots on them, but it is pretty freaking silly that it would all work together if they did.
I think it is reasonable to assume very powerful wizards might eventually get both a Robe of Archmagi and one of the other items like a staff or wand in the same campaign and want to use both, for a combination of +5 and that is pretty broken.