You keep asking for general strategies, but you’re just handicapping yourself to the point where most people in this thread can’t even help you. From what’s been said in this thread the only thing I know about your opponent is that he spams AA Fireballs and you’re either not good enough to realize jumping is bad or something is missing.
How does your opponent play? Does he constantly attack you? Does he stay out of your range and poke you? Does he turtle and fireball spam?
Help is best given when you are specific. You aren’t playing to win anyways. You say that you want to win fairly? Kara-canceling is a legitimate strategy and from what I know, Capcom has not said anything about Karas being a glitch. They did after all give a certain character (*ahem Makoto) a move that is pretty much canceled by everything except for a universal throw and other normals (as opposed to being able to cancel into universal throws from the starting frames of any other normal).
Well anyways, I don’t see what you mean by Gill not having a good wake-up. If you’re shooting off uppercuts on wake-up all the time, you’re not that good anyways. He should be watching you and be doing the typical throw if you’re too close, block or mash c.lk, c.mk, c.rh on wake up if you’re not anyways or be blocking if you’re doing backstep, forward throw or whiff/tick throwing him.
Anyways, to address strategies to beat Gill with you have to know that even if your opponent is not even half as good as you, that still doesn’t change the fact that Gill has near instant high priority moves that WILL hit you. Parrying helps, but in general it becomes very hard to rush him down if your opponent is even remotely competent.
If he stays away and just fireballs you, you have to learn to parry. Either that or pick a character that has good range on pokes, good projectiles or good ground distance covering moves. Good candidates are Chun Li, Yun, Akuma, Remy or hell, even Ibuki.
Chun Li can dash in on AA and use f+HP which is pretty fast and has quite a bit of range. You can do the same thing if he switches to a ground fireball, jump over and f+HP. Knocking Gill down and harassing him with throws, s.RH and other things until you have the meter for anything xx SA2. c.LP, MK Kara LP+LK works really well as well as walking back out of throw range and MK Kara LP+LK, but whether you wanna learn to use competitive techniques or not is up to you.
Yun is kind of the same, you can shoulder under the fireball if you time it right or just learn to jump and dive past the fireball. c.MK x LP shoulder is probably the safest thing you can do as it has the most range of what you can do to cancel into GJ (SA3) safely, or you could just do c.MK xx SA3. Continue with GJ pressure from there. OH hop kicks and walking forward c.LKs work well until you hit him and you can go into a GJ string from there. If you’re getting AA fireballs at midrange you can just lunge punch him in the gut. Pretty standard stuff.
Akuma can do well against scrubby players in general. Air fireballs should be wake-up only as Gill’s AA is 2 hits and most likely will be hitting you if you both shoot off fireballs. Best thing to do is probably to just jump or demon-flip (K before hitting the ground to move quickly) over fireballs, pressure with RH Hurricane Kicks and throws. Abuse sweep at max distance and see if he responds or punishes. If he doesn’t, keep doing it, jump up air fireball on knockdown, dash forward and either go c.LK x LK Hurricane Kick etc or f+MP (OH). If you’re using Akuma, best super is probably SA1. If you really have to, super through his ground fireballs or if you’re close enough and he starts randomly shooting AA fireballs.
Lastly Remy can be useful as well. He has a lot of forward moving or long ranged pokes (f+HP, s.MK, j.RH). Low sonic boom spam and j.HP, s/c.MP x regular/EX high/low sonic booms can work. I doubt your opponent really even parries at all and it’s good to keep the pressure on him. If you’re not as adamant about learning to at least use Karas, try j.HP, close s.mk, RH Kara LP+LK. Pretty hard to do consistently, but well worth it if you learn how to do it.
There are others that can do well, but that’s dependent on how your opponent plays and also with how good you are yourselff.