“Outlier” is a cop-out argument with no foundation, and you only selectively apply it to scenes you don’t like. And yeah, he doesn’t scale remotely either in AP or LS, given that you couldn’t refute my point or provide any argument for why he would have randomly become massively weaker, especially when Shinigami simply don’t weaken like that without an actual reason.
No, calling it an outlier isn't a tactic. I assumed you knew the explanation. Grimmjow doesn't have an anti-feat that shows he's NOT strong enough to hit Askin. Chojuro, however, does. SS Arc Shikai Ichigo defeating him would be an anti-feat in that case. Unless, of course, you're saying Chojuro weakened.
Why would Chojuro's weakening be minimal? Is there direct evidence that stopping fighting causes a small power drop? Just like with Yamamoto, there's no evidence that he trains every day. We say Yamamoto didn't weaken because of the statement that he trains every day. But this wasn't stated for Chojuro. Byakuya stated that Chojuro compensates for Yamamoto's weaknesses. Yamamoto isn't lacking in strength. Therefore, Chojuro doesn't need to improve his strength.
Note: It might have been someone else who said this, I don't remember exactly.
Also, since there's no information on this wiki about Baraggan training, Young Baraggan was accepted as > Old & Espada Baraggan. Espada Baraggan wasn't upscaled because of Young Baraggan's fight with Ikomikidomoe. So yes, stopping training can cause more nerfs.
I see no difference between Chojuro’s backstab and Grimmjow’s one.
Yes, there's no difference; both are off-guard type combat attacks. However, as I explained above, while Chojuro has an anti-feat, Grimmjow doesn't have an anti-feat that shows his TYBW and CFYOW forms are far below Askin level. For example, you'd be right if there was proof that Ginjo and Sealed Ikomikidomoe were too weak to hit Askin.