You're missing the point...but it's pretty hard to really show that to you.
One of those "you just have to find out for yourself."
Unfortunately, that takes time and effort.
But consider this [as far as you thinking you'll "never get good"...I'm not taking that too literally since you're speaking in generalities, but humor me for a second]:
Chances are pretty good that if you're playing ANY Smash game competitively, Brawl in your case, a year or two down the line, you will still be playing.
Correct? [hah, well whether you think so or not, I'm pretty **** sure you will be...you've already been sucked in XD]
If you're unconfident about your potential in Melee to become a "worthy contender," then consider this: People like Dr. Peepee who have been playing for 2 years and are already considered "pro" are anomalies.
But at the absolute least, look at me? If you subtract my time spent playing Brawl heavily, I only have a year and a half of Melee under my belt, and I can definitely hang with GA's finest [lol, beating all of them is a different story, but I'm no scrub.]
Also...you're playing Brawl.
There are a lot of pros out there. While you get better at Brawl, they're also getting better and solidifying their dominance. It'd be the same thing as if you were playing Melee [okay okay that's kinda misleading since there are way more high-level Melee players than there are high level Brawl players]. By your logic, there's some similar degree of "pointlessness" to you continuing to play Brawl.
Don't give up. And don't make bull**** excuses for yourself.