Except for the part where it's NOT true.
Sure, early on in the show's run you could buy that, but as the seasons go on (and on and on and on and on), he makes no progress whatsoever, making him slowly de-evolve into an incompetent doofus who still has no clue what it takes to improve, or worse, DOES know what it takes but refuses to do it because of some invariably inane bullshit. And his infamously middling *coughcough* track record at evolving Pokémon isn't all there is to it, even when any normal person would've said "fuck it" and shoved a Thunder Stone up Pikachu's ass if necessary. His marketing-required team reboot at the start of every generation didn't help, either - in fact, it may be the worst offender, as the one time Ash legitimately looked like a force was when he had almost every Pokémon he's ever had on hand (including a lot of fully-evolved Pokémon to boot). Of course the outcome was history, he was eventually stopped by
But I'm just rambling on. Point is, he's had 17 years to show some improvement, and at the end of the day he always stays near square one. Weakness stops being weakness and turns into something much worse when you never learn from what you did wrong. As for being relatable... well, I can't argue against that. If you identify with him, then what does that make you?
Still, why are all the pro-Ash zombies coming out of their caves now? Is it because Smogon's ladder is so flooded with casuals that they can actually perform decently well using nutty garbage like Eviolite Slowbro, Hyper Beam Sylveon and Ash-based teams by beating the enormous amount of similarly rubbish players, leading them to believe the old doctrine of fighting with your favorites, treating your Pokémon with love and care and all that sappy rhetoric is the key to victory? Is it because some people were outraged by that one picture that had shots of Legend of Thunder, Pokémon Origins and the mega evolution special, that said that all you needed to make a good Pokémon anime was removing Ash, and every brainless sheep who thought they were making good points followed suit?
Either way, that won't change anything for me. Ash Ketchum sucked back then, he sucks now, and he'll suck forever.