Well, what HELPED to make them so powerful were tools that were relatively safe that they could more or less use at Thier leisure (and spam them as well) that carried amazing risk/reward for them.
So Chun had instant air legs. She still does granted but they are negative on block now.. A Chun player could get in your face and pressure with anything she wanted and get throw after throw after throw and offense after offense after offense because of IA legs. They were safe, they totally avoided a HUGE number of buttons, would shit on throw techs and could lead in to a combo that while not insanely high damaging or anything was still respectable. She could just mash them out and they were extremely difficult to deal with. If you KNEW they were coming, towards the end of the season players were reacting to them, some characters could check her, bit not everyone and even then it was a risk. Chuns offense once it got rolling, was completely bullshit. Add in her other tools (st.fp , a reversal, solid fireball, etc) and she was just oppressive.
Mika had Whip and her corner-anywhere bounce on top of fast gap closers that could.be spaced out to be safe and of.i remember correctly, plus. Once a Mika was.in whip range they could literally spam the move until it worked. Even at high level play Mika's would do this, because why not? One touch and she could put you in her blender where one additional wrong guess was absolutely a stun and most likely the round. You could CC a Mika and full punish and the risk/reward was usually STILL in her favor. Couple.yhat with her bonkers mix-ups, massive straight damage, huge ex throw damage and range and.other tools and you had a character that once she got in (and she had excellent tools to get in.. a gap closers on a GRAPPLER that leaves you plus is a nightmare) she could do whatever she wanted and even if you were ready for not and actively countering it, she could just mash through because the risk/reward was monumentally difficult to tilt out of her favor.
Throw nerfs were important in timing things down as well but I can't remember what Chun and Mika got after reg throws so I can't speak too much on that aspect.
As to Bison, he got a 3f button and various other buffs including a walk speed buff (yes, as slow as he moves, that speed used.to be even.worse) . Bison is very good this season, very, and he's super fun.
