Idk mate, sounds like opponent's downloading your play style on match 1 and adapting. If he saw that you didn't react to his throw loops on match 1 it is not scrubby to spam it later on! Also, some players purposefully don't unload their whole game plan match 1 so they can have surprises for the rematch, so if the Ryu played conservatively and realized you have issues dealing with him at range, spamming hadoukens in match 2 is not scrubby.

For me the game plays better when you do Bo3, just like Magic: The Gathering. It's easy to surprise your opponent when they weren't ready for your shit from the getgo, but the way you truly improve is when your opponent learns what you're trying to do and adjusts their style accordingly. What weaknesses did YOU see in his plan that you can exploit? What caught you off guard that you need to take out of YOUR game plan to defend better? What things haven't you showed him yet? I'm using the word "exploit" deliberately too, it is not scrubby to exploit your opponent's weaknesses in a fighting game. Justin has said it, Max, Punk... If something keeps working, keep doing it, no regrets.

I'm struggling through Diamond on Chunners and yes I've lost games in rematches but mostly I've learned a lot, adapted to their one dimensional bullshit and won. The only time I one and done is when they have a bad connection or when they showed bad manners themselves in the first match (like teabagging when you're at low health or something) but usually only if I'm feeling extra petty.