It depends on your definition of stale. This is the perfect case of Vince and the shitty writers needing to gtfo and let someone with 20 years in the business who knows what he's doing go out and do it. He needs to sell this storyline.
JUST depending on the Yes/No has made him stale. It should be a part of the character and used whenever it's welcome, but in every single promo they're doing all this stuff to basically force him to say yes over and over, or he's just doing it anyway. That's stale. The issue with the character imo is that he's incapable of anger and doesn't care. He gets screwed by the Authority at Night of Champions? Yes, yes, yes. Gets attacked by Big Show and has the Authority screw him over again? Yes, yes, yes. Gets attacked by his mentor and screwed out of the belt yet again? Okay, he sold that for one week when he snapped on Shawn. Gets kidnapped by the Wyatts? Is perfectly fine the next week, just yessing his way down the ramp... It's really hard to get behind a character when they don't seem to care about all the bad shit going on around him. That's not a stale character, that's bad writing.
Luckily for Bryan he's a good enough performer and a likable enough dude that people will either see past that and like the guy anyway, or are just used to lousy characters from this company and like who they want to like.
And him having the same main event move loop as the rest of the faces isn't helping, somehow the Five Moves of Doom are attached to Bryan now instead of Cena
