Bulbagarden

Well, that too, but it's something I've recently noticed. They never make episodes focused on Team Rocket anymore, it's always about Ash and his friends now while the TRio are treated as essentially obstacles rather than antagonists or actual characters anymore, as if they're just THERE simply to pad out the episode rather than actually contribute to the plot.

It is not like that is something never happened before. Excluding Kanto and first half of BW, basically TRio were never ever "villains" nor "antagonist" in the characterization sense. They are indeed "villains" and "antagonist" in terms of role-play, but other than their role, their characteristics and personalities makes them unqualified for such role. Basically, they are just Creator's Pet use to steal screen time, they are never there for important plot.

Well it's also because they just feel like there's no purpose to them anymore, even as "harmless villains" they seem to have no purpose. In the earlier seasons, they weren't simply antagonists or obstacles, they were actual characters that were interesting in their own rights and had actual character development at times. Heck, some of the TRio focused episodes were the best in the series like the one where Meowth learns to talk or we learn that James is rich.

Now they have almost no episodes of their own and they're only really just there to force an episode to be longer. It's not that they're bad at being villains, it's that their characters aren't interesting anymore like they used to.

ttp://ultraericthered.tumblr.com/post/59459381818/team-rockets-characterization-marches-on-again
They had long been flanderized, and I'm guaranteed the anime will follow the old flanderization trend as it was from OS TRio to DP TRio. Just you wait and see, the SM TRio will be even more pointless than now.

The main problem is, they are already the creator's favourite pets, they are too well-treated by TPTB. Despite that they don't contribute much to the overall main story, only appears to produce silly troubles, they have their own radio show and albums, and they are used as mascot for anime marketing more than any other characters in the show. So no matter how the fans hate them, TPTB will not do anything to improve them permanently as characters.

Well even hardcore fans of the TRio don't even like them anymore, on BOTH sides of the Pacific, let alone the American fans, though I'd rather have them stay on the show rather than have Ash continue being the main character.

You want TRio become more important than the protagonist? I wouldn't want to see that though. Ash remaining as the protagonist for me personally is now more on the two-sided option. They may replace him with someone else or continue using him, I wouldn't mind either case. Story-writing and characterization is rather my main matter of concern.