Yeah, let's ignore regular GIs. Sure, Yoda has an advantage there as he can 1_3 GI everything and be assured it will work, but Yoda doesn't really count, and we all know that.
aGIs do count, as they vary from character to character. Their utility, damage, setups, active frames, etc. So aGIs do differentiate characters where GIs do not.
I just recently discovered the Auto-GI thread. That's helping me to answer this question. I had no idea Kilik's Asura TCd, TJd and GId mids. He's invincible!
I really am looking for a character that you could win rounds in a row with, always evading and never blocking. Now, any character can get lucky and do this once or twice, particularly in a situation where one player clearly dominates the other. But obviously we're talking even matchups re: player skill. Hope that clears the topic up a bit.