We only really played in IGAU as far as lots of games. Didn't play much in MK9 and didn't really play much vs my SZ.
My style with Aquaman was knock you down and keep you there. If I couldn't get knockdowns then I normally struggle with him. Defense online also goes out the window. Had to resort to random B3's to stop you from jumping outside of uppercut range when normally I would AA J2 on reaction to the jump. Also couldn't D1~Rush after blocking B1/B11 because 33, another B1, etc would still hit. Normally you would have to D12~MB Tiara which I can trait out of which forces WW to burn meter and still not launch Aquaman. She could also do 23 and Trade with my D1. This tactic will force WW to never be able to loop he B1 frame trap or get me to take a 50/50 attempt. The meta wasn't really able to expand online which sucks vs a very smart player like yourself. I was also able to hit you with B2's which is complete online bullshit. It was just a crap shoot online.
Of course, if I get knocked down in the corner it was a messed up situation. I could trait and block high which protects me from the 33/b2 but if you dash up and F3, I get crossed up and launched for a combo and end up in the same situation, now without my trait. I could wake up attack to beat the dash F3 but that will lose to a properly timed B2 which also prevents me from using trait and wake up attack. I could guess cross up but still get hit by the non cross up F3. These are just a few of the many scenarios that exist here. It's VERY HARD to "make a read" when there are this many scenarios. This is why IGAU comes down to more pure guessing then pure skill or pure ability to make the better read.
IGAU came down to coin flips (using a 5 sided coin in some instances) without consequence for many characters. Many players that struggle in other fighters could find it a bit easier when so much is based on the SAFE 50/50 where as many other games would punish you heavily or just not even have many (if any) 50/50's. Because of this it could be argued that its actually harder to be good in IGAU due to just how much pure guessing situations you find yourself in. Its always up for debate.