I feel like part of the issue that can spawn that kind of mentality is that the goal of completing the Pokedex in the games increasingly became a secondary concern as more and more games came in the series and time went on.
Completing the Pokedex is pretty fun in PLA imo, and I'm really enjoying my time with doing so thus far. That being said, this isn't the first time completing the Pokedex was meant to be a primary goal of a Pokémon game. In fact, the thing with that is that the goal of completing the Dex was a core aspect of the original Pokémon games: Red and Green (or as the rest of the world knows it, Red and Blue). Gen 1, the very first Pokemon games ever, had completing the Pokedex as one of the goals of the game. After all, as already mentioned, the catchphrase "Gotta catch 'em all" was prominent back in Gen 1. Professor Oak even made it clear at the beginning of the game that he gave you the Pokedex with the goal of wanting you to catch all 150 mons in Kanto and create a complete and comprehensive guide to all the Pokémon in the Kanto region. Catching them all was a major goal to do in that game, besides the whole "Beat 8 Gyms, the Elite Four, and become Champion" and whatnot. Still, catching every mon in the Pokedex and completing it was a goal that was the core of what made RGBY what they were, and an explicit goal Professor Oak said back then. The games were made to be played by catching them all, and the Gen 1 mons were designed with a power curve so you would box earlier catches for later ones and whatnot so you always had room for every mon out there. Moreover, RGBY and their remakes FRLG and LGPE even reward you for successfully catching a certain number of mons at various story checkpoints with Professor Oak's aides out there waiting to see if you've caught a certain number of mons and giving you a reward in return, FRLG even requires you catch at least 60 to unlock the National Dex and postgame, encouraging you to catch as many mons as you can.
That being said, as time went on the goal of completing the Dex became more and more of a secondary concern as the games in the series started to focus on other things. Now there's post-game battling that only certain mons can survive in, whether it be battle facilities or VGC, and the games from Gen 4 onwards have focused more on that aspect, and also nowadays Pokemon games really push the notion that the mons you catch are your friends and partners, which really encourages you to stick with the mons you use as well as just use the mons you like/want. Nowadays there's also more focus on interacting with your Pokemon outside of battle and playing with them too, which reinforces this, as the games since Gen 6 have had ways to play with your mons outside of battle and whatnot, PLA itself does have this though.
Of course, that's not to say that the goal ceased to exist, but in games after Gen 1/2 that became more of a secondary concern and afterthought than before. PLA is going back to the roots of a core aspect of Gen 1 and making it a primary goal of the game, but after so many years of enforcing the mentality that Pokemon are your friends and partners and the games going in a variety of different directions after Gen 3, the "Complete the Pokedex" mission is practically less of a concern for many people and so for some people that might put people off of how PLA is designed. Plus, the other thing is that the audience that enjoys Pokemon has grown much larger over the years and the franchise is so long running with so many games that do different things now that people will always value and prioritize different aspects of Pokemon: everyone's reason for playing Pokemon is different. Yes, some people still do make it their personal goal to complete the Pokedex, but that's not the entirety of the audience who plays Pokemon. So PLA might be a turn off for some people by taking that aspect, which was mainly a core goal in the Kanto games, and making it a core goal in this game, of course with some major changes to how you complete the Pokedex.
With all that said, I don't think PLA's whole Pokedex being a core focus and the way you need to do research tasks for each Pokemon and whatnot will be something that fully encapsulates every mainline game going forward. I said it in another thread, but I think we may see a wider variety of mainline Pokemon games taking different directions going forward: we already saw it with Gen 8/the Switch games thus far, with Let's Go: Pikachu and Eevee as a Pokemon Go-styled game, Sword and Shield being a "traditional" mainline game, and Legends: Arceus being an experimental action adventure RPG, and Gen 9 could have a similar degree of variety. I don't think the traditional mainline games at this point are going away anytime soon: the base Gen 9 games will probably be closer to SwSh and past mainline games in terms of design of traditional 8 Gyms+Elite Four+Champion and becoming Champion, having a battle facility, other minigame features, and multiplayer as well as an official VGC and BSS format. I think every generation from here on will have at least one of that: that's not going away anytime soon. But from there we could see some more experimental titles existing alongside the traditional ones. I don't think PLA by itself is indicative of what every mainline title will be like moving forward: sure, Gen 9 will probably adopt some things from PLA gameplay wise, but I'm sure it will still largely stay close to a traditional mainline Pokemon experience.
