There are gloves that only the barbarian can use.
as i said:
-_-
A drum that does Thunderwave or a Violin that can put someone to sleep. Things like that.
The problem is that any drum you have "does Thunderwave" since Bard is casting through his instrument. :-/
And excuse me ... but everyone know that the only instrument that put others to sleep is Harp!
Allways was, allways will be. :P Sometimes even in reality.

These bard items don't feel gamey to me. They make reasonable sense. It's basically a buff to the inspiration, adding an additional benefit.
Really? O_o
You fiddle so hard so your friend gets inspired by your preformance and makes one better attack, or defensive move, or he manages to pick some extremely coplex lock ... but only one of those.
And if you fiddle as hard with this hat on your head ... he is so inspired so his wounds start closing themselves ... and if you also wear this armor, your own wounds are so inspired by that so they start closing aswell.
Something like that "dont feel gamey"?

We have different definitions friend.

It also makes sense that someone would create the items in question. They're reasonably useful.
As opposed to, say, an axe that does increased damage if you're at half hit points. That's a limiter that feels more like it was put there by the DM than by the wizard who created the item.
I gues this depends hardly on one imagination ...
I for one can imagine Necromancer who theorizes, that blood contains energy, and when wearer of some magical artefact inevidably gets hurt in combat, that energy is wasted ... so in order to test his theory, he created this enchantment that gather energy from wounds ... and once it gather enough, it expells it.

What a coincindence that required amount of energy equals 50% of some imaginary number that have no relation to your actual health or injury.

But cant really imagine any Wizard thinking about creating item that will heal other people and the artist when they feel "inspired" by beautifull music.

I'm not a fan of items that are underwhelming when compared to their presentation. For instance, Phalar Alluve. Additionally, all the adamantine weapons and armor.
I would be fine with those items if the story presented them in a different manner. If the game didn't tell me the adamantine items were the greatest items ever, then I wouldn't be disappointed to see them. If the game didn't present Phalar Alluve as being buried in stone and then levitating out after a blood ritual, I wouldn't be disappointed.
Some time ago i suggested "fix" for Adamantine ...
Since that one bothers me aswell ...
In my suggestion, i wanted Larian to simply add some journal that would explain that this is actualy NOT Adamantine, but only some weaker material that can "seem" like one, at first sight ... but even tho it never reach Adamantine quality, its still good enough for both weapons and armors, so the forgemaster decided to take this secret to his grave and continue in his work ...
Simmilar as when you put side by side proper "Damask Steel" ... and so called "Tin Steel Damascus" (even tho there is HUGE difference in quality in this example) ... on first sight, you would never guess the difference (unless you know what to look for) ... but when would you start comparing them, you would find really quicly that one is faaaaaaaaaaaaaaaaaaaar better than the other.

As for Phalar ... im still convinced that finding +1 Longsword in exchange for single diceroll (and not even hard one) is appropriate reward.

In my opinion, the drawbacks should still be there, but it would help if there were some way to mitigate the hurt. For instance, maybe the Light of Creation doesn't hurt the user if the user is wearing the ring that protects against being shocked.
Maybe the hag's staff doesn't hurt the user if the user has the Hag's Eye condition.
Ehm ...
Light of creation dont "hurt" its wielder, it have chance to stun him.
And Hag's Staff gives only 1d4 Poison damage, wich can be easily mitigated to half by potion, being a Dwarf or Halfling i believe (but not sure), or by simply wearing Poison Resistance ring ... and personaly i would never trade 1d4/2 damage per attack for change to strike crittical damage with this staff.

(Not sure if you remember ... inability to cause critical strikes is one of effects of Hag's Eye ... and that shit is PERMANENT ... pretty serious stuff. :-/ )