Okay hear me out.
What if Rook's super had invincible startup and then it went to super armor in active frames?
The difference between invincible and super armor in practice is huge, besides just the fact you can be damage.
Right now Checkmate Buster loses to windmill because windmill is slower. I haven't checked, but it might lose to Midori throw and I think it loses to Setsuki super. Maybe other invincible moves too.
Rook's seen a lot of nerfs over a course of many iterations, from reducing the range (fair) and then changing it from invincible to super armor (also fair I suppose) and from what I heard he had a cancelable B dash way back when. But now that his C grab can be beat, it feels like he's a good bit weaker. I still think that checkmate Buster shouldn't lose to other special grabs though, and it wouldn't change much for most other fights, but it's just something I'm thinking about. I suppose a lot of what I said is irrelevant but I'm sleep deprived and I'm thinking about Fsfg instead of going to bed. Cheers.