"Reaction spells are in high demand on Wizards and Sorcerers. Bards don't have Shield, Absorb Elements or Counterspell, and Silvery Barbs is also available to anyone who picks up the very very powerful feat Fey Touched, and Clerics/Paladins have no reaction spells while the other casters only have one of the decent ones.

Nothing is gamebreaking in D&D. It's a big and very unnecessary buff to Bards, Wizards, Sorcerers and Clerics/Druids with Fey Touched. Will D&D be a slightly better or slightly worse game by its introduction? I think worse.

https://www.youtube.com/watch?v=Iywz0U5Zwl0

Without getting into the minutiae of this spell and its interactions with everything else in the game, I think something that is overlooked is that a new addition being good or bad for the game is not necessarily directly related to its power level. It can be the type of gameplay it encourages, the overshadowing of other abilities, bad wordings and the shenanigans that will ensue, etc. People often justify the opinions they have by trying to make them "objective", calling things overpowered or imbalanced, but this is not always the real problem. The first version of Healing Spirit didn't pose any problem in combat, but was an absolute mess out of combat. Silvery barbs encourages and optimizes the use of save&suck / save&die spells, and in doing so will favor more swingy combat encounters, which makes balancing them harder for the DM; it bring some power creep to mid-level full arcane casters, who are already some of the most potent characters in the game. So in my opinion, it doesn't have to be broken/overpowered to have a potential negative effect on games, and be better left out of the spell lists.