When the opponent can punish your fireballs on reaction, you’ll have to adjust your game accordingly, but often it also opens up options, depending on your opponent’s skill.
If your opponent is waiting for you to throw a fireball, that usually means they’re focused on reacting to it. Therefore, you can get away with other things, like a quick dash in c.mk, or maybe even a jump. You might also be able to make them react to a bait. You can also try to surprise them with close range fireballs, though if the opponent is really good, those will get punished too.
It’s also a good time to pretend you’re Zangief and just walk forward. The opponent might be so focused that they forget to fight for their spacing. Put them in the corner