Okay, imma give some advice as best I can since you seem pretty depressed and mopey. It'll come in two parts.
First:
300 hours pretty much totally fucking wasted.
I've seen this kind of attitude from several friends, and I've never seen it end well.
First off, time is never wasted. If you really like the game, you should be able to enjoy it regardless of whether you're doing well or losing. In fact, competitive games in general are not for you if you really don't like losing. There are always going to be people above your level, and even the best pro players admit they lose a LOT. If you really love the game though, you shouldn't care about that, because just playing should be fun enough as it is. One of the best speed runners out there was asked how he feels when he gets screwed over midway through a run, and he responded that he doesn't mind because he loves the game so much. I doubt he would have put in the time and effort to master the game if he really hated what happens to you in 90% of your runs. I've also seen a lot of people with big aspirations rage quit and become apathetic because they just don't have enough patience to improve and soldier through tough times while still enjoying the game.
Second, you are not
that bad. I have played a lot of quick match rounds against players who barely knew what they were doing, and who you could beat easily. I'd call you intermediate because you at least seem to know what you're doing and put up a fight. It should not be a problem for you to find players whom you are equally matched against, if you can't than you are probably looking for people who are too good.
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Now for part 2: improvement.
There is no magical strategy guide out there that will make you a better player overall. There might be some magical bit of advice that will help you improve, but you will never find it in any guide or any critique because it's something for you personally.
To give an example, several years ago I was really struggling to improve (I wasn't frustrated though, see above). And no matter what advice was given or how much I played I never seemed to get better. There actually was a reason for this though. You see, my understanding of fighting games was very self taught. I came to them off of games where you could always avoid damage if you played correctly and had sufficient reflexes/execution. As a result, I developed this philosophy of "playing safe". Trying to find tactics that I thought couldn't be punished so long as I didn't screw up the execution or failed to react to something. Yes, I knew about dp's and psychic super reversals and whatnot, but in general it was kind of a guiding principle to me to always try to "play safe". As a result a lot of people would often say that I was decent but very "predictable" and lacking "creativity" and incapable of punishing or dealing with certain strats. Ultimately it wasn't that I couldn't be creative or unpredictable, just that I was playing the wrong way.
What I didn't realize, is that playing safe is utterly impossible in these kinds of games. Even beyond unsubtle things like dragon punches and whatnot, there are a million ways to punish even the safest poke (wiff bait, stuff on start up by doing a similar move at close range a few frames before they hit the button, etc.) When I finally realized this, I threw the "safe" strats in the trash and definitely started to improve. Not only was my game plan less one dimensional, but I could start to see how seemingly insurmountable defenses and offenses could be punished if you could outread them and were willing to take risks. It still took a while to get better, because I was still accustomed to one particular play style with a few types of characters, however I started to improve more once I just picked a top tier and started learning how to put all those tools and options to use, which helped me with other characters and other games that I wasn't as acquainted with.
In short, finally realizing that dashing in and doing a poke was not fucking safe was all I really needed to move onto the next level.
Now, there might be something like that for you, though not necessarily the same exact issue. Some mistaken thought process or self imposed limitation that is holding you back, and only you can figure it out. However, if not than it can only be blamed on one thing: Fundamentals
Contrary to what some people believe that everything is just game knowledge, muscle memory, and memorization, skill does exist and makes a very heavy impact. As far as I know, nobody (or at least very few people) are born with lightning fast reflexes or precise execution. It's just something you have to work on and work on, and it'll be such a subtle change that it sometimes won't feel like your time is being rewarded. Again, that's why you have to love the game.
Different people also improve these skills at very different rates, there's no scientific formula for just how many times you or anybody else needs to practice a combo or blocking an overhead before you can do it more consistently. You just have to stick with it and enjoy yourself and have faith that you'll improve over time. And if you don't improve over time, maybe try a different character or check for any self imposed limitations again.
Anyway that's all I can really say. Turn off the Linkin Park in your head and put on
something more rousing. Enjoy the game, keep trying, and you'll get your moneys worth one way or another.