See, I'll counter this with a few points.
1) Wearing Studded Leather armor is the exact same bonus to AC, normally. Now, you could argue Mage Armor, which allows you to stack the bracers and the equivalent of +1 Studded, but there are other ways to do that if you really really wanted to. Again, see Staff of Power. Very Rare attunement for +2 AC, +2 Spell attacks, +2 Hit and damage, a charged strike, and a selection of spells. WAY WAY better use of an attunement slot.
2) Just.... don't make it available if you have a Bladesinger. See, I'm not a fan of designing items to restrict them based off of a single subclass in existence. If you feel like a Bladesinger is too powerful with this item, then just don't give it in treasure to a bladesinger. But, right now, it is not useful enough for the people who can use it without it being broken.
And, to clarify, it isn't that +2 AC isn't a big deal. It is how it interacts with everything else. This is an item that is useless for the majority of classes. Take a Rogue for a moment, and give them the option between the Bracers and +1 Studded Leather armor. Both are Rare items, the bracers require attunement. The Armor makes their AC calculation 13+Dex, the Bracers make it 12+Dex.
And, when it narrow it down to who can use it, you then see a comparison. If a fighter picks up a 10 gold shield, they get +2 AC. IF a monk picks up a 1,000 gold Bracer of Defense, and attunes to it... they get +2 AC. This item is literally just a shield for characters who can't wear armor. And... that doesn't sound that impressive to me. Not when I compare it to some of the other defensive items in the game. Like say, a +2 Shield which DnD beyond lists as Rare, with no attunement. Which is literally the same effect as wearing these bracers on top of a shield and armor set.