They all have their place in single player, I’ll admit, but none of the main four have done anything to help one of Pokémon’s biggest issues, that being the fact these games are just too easy for their audience these days.
If I'm gonna be frank: Pokemon games were never truly difficult. I have two points to raise here, and I think one of them is surprising but SV's Raids have made very apparent for the past half year or so.
First is that Pokemon games aren't and never were hard, and even the older games were pretty darn easy. Once you have a full grasp on the depth of knowledge of Pokemon's battle system, the game isn't truly difficult unless you make it so yourself. Older games just had an artificial sense of difficulty because of bad game design, aka jank level curves and limited pool of good options for the player. Tedium and demanding long term old school grinding does not equate to genuine difficulty.
The other is that the target audience of the franchise is young kids who are in elementary school. And believe it or not, you may not realize it as a Smogon player with knowledge of Pokemon's battle system and its nuances, but the average elementary school kid actually substantially lacks knowledge on Pokemon's more nuanced aspects, and as such Pokemon would actually feel difficult to them because of it. You'll hear many stories across the internet about SV's Tera Raids nowadays, but boy you'll be surprised at how truly incompetent the average player who is actually part of Pokemon's target audience is: they have little knowledge of type matchups, and Terastal itself is actually too complicated a mechanic for the average kid to understand, because you have many cases of players either choosing their Raid fighter based on the original type of the Raid Boss, or choosing based on the Tera Type without accounting for the original type, or worse, simply choosing a powerful boxart legendary because they think it's godly and invincible.
There are many stories about it, but if you think the actual target audience of the Pokemon games finds the games easy...boy do I have some news for you. The Tera Raids in Scarlet and Violet and the countless stories people have with them have been incredibly revelatory in terms of how genuinely incompetent the average Pokemon player actually is: most of them actually wouldn't find these games as easy as we hardcore competitive players do, and in fact their playstyle lends to a much harder experience.
That being said, I do have one extra critique for these mechanics, but it’s probably not what you’re expecting. Can we even call these “generational” anymore? I’d go as far as to say ever since Sword & Shield, not even the game developers can properly define what a “generation of Pokémon” is. Gimmicks, these still remain either way, but a little consistency would be nice.
The game developers have started to diversify from the standard RGB formula in terms of mainline games, that said a generation can still be defined by a new region, with a new set of starters and a new roster of Pokemon in a base paired release games. Sword and Shield is by all hallmarks its own generation with Legends: Arceus being a mid-generation game within it, the generation lasted three years, the anime had its own season lasting its duration.
Scarlet and Violet also marks the beginning of a new generation, a new anime series started in it, it stars a new region in Paldea, with new starters and whatnot. And a new manga series focusing on it is starting soon as well.
How they're making the games is changing, but generations are still clear to define based on the factors of new starters, new regions, new anime series, new manga, the Trading Card Game, and so on.