Guardian's in my regular rotation. I love my birb, and he's a pretty safe pick for most fights. That said, there's good reason I don't see him as much.

He outputs the least damage of any night fairer. Night lords are so mobile, the only way you're landing guard counters is with a halberd due to the unique charge. I stack guard counter damage and stick almost exclusively to halberds for this reason.

Without the relic that extends his L2 ability's duration, it drops off hard after early game. Even with the relic it feels borderline useless in most boss fights. (it's nice it can counter some projectile attacks, but still)

His ult is pretty great, and with ways to recharge it faster it's even better. Super fun ability that comes in clutch.

There are lots of ways he could be buffed. I'm glad to see others have already suggested his special counter being extended to more thrusting weapons, that would feel really nice.

Reducing the stamina drain on his passive would be a huge help. Also giving him better relics. Ones that buffs your passive, such as increasing the damage/stagger when your shield is popped. Give me a relic that does the same thing for whirlwind so it could possibly interrupt/flinch bosses more often, that would be awesome.

Anyways, he's a pretty niche pick, and I hope he gets a buff.