It's very hard indeed not to have expectations, but past successes are no guarantee of future successes unfortunately. Although at the same time, if you want to be optimistic about it, one bad game does not mean that the game that follows it will be bad. Each game can and should be judged for what it is in itself, outside of the context of its series. If you find it difficult to not have expectations of games, try instead not to compare them to other games, perhaps. Instead of expecting a game to be as good as another, just go into it hoping you'll have a good time, and stop thinking "this could be better" or whatever else. It could always be better...but it could also be worse.
For Game Freak at least, it's not feasible because they are a very small team and are notoriously inept when it comes to programming; they always have been. They also have to work to TPC's schedule when it comes to releasing games, because Pokemon is not about video games, it's about merchandise. Pokemon is also a major system seller for Nintendo, so they can't afford to take their time between releases. Plus with Masuda strangling their resources with his preference of working in smaller teams, and Nintendo's policy on crunch culture, they can only do so much with the time that they have. If you look at any other AAA title - because Pokemon is a AAA franchise, whether TPC want to admit it or not - they'll have significantly larger teams, will outsource parts of the work, and they'll take a lot longer to make the games before releasing them. Game Freak simply don't have the time, the manpower, or the technical knowledge (at least, not right now) to take full advantage of the Switch hardware. But that could very well change in the future, as they've now been working with the Switch for some time and are going to be more familiar with the hardware. The troubles with getting the 3DS models over to the Switch aren't going to be problems they have with the next set of games, so they'll be able to devote more time to other things. Presumably they'll be able to do that elsewhere as well. So the quality could improve with future titles.
Square Enix are a little more complicated to dissect, but I think with Kingdom Hearts III at least the most important thing to look at is the development time: KHIII was in development for at least 6 years, and a lot can and did happen between now and then. I mean, Final Fantasy XV started life out as Final Fantasy Versus XIII on a different platform and was a completely different game. Ideas change, things get scrapped and moved around, priorities change to other things, and so on. What Kingdom Hearts III started out as and what it ended up as are likely very different products. As for the repetition of worlds and concepts, I can only assume this was to tie up story arcs (at least, they certainly did that with Olympus IIRC, which was in most of the games) or to pad things out because they couldn't incorporate everything they wanted to due to time constraints, budget, or maybe even licensing problems since it's Disney.
A lot of this is speculation on my part, because I don't work at Game Freak or Square Enix, but it's easy to infer things from interviews, demos, trailers, and what little knowledge of the structure of the companies and their games that we have. If you want to be cynical about it - and let's face it, there is probably some truth to this - it's also because they don't NEED to put effort in anymore to rake in money, and that is all companies care about: making as much money as possible. Games with high expectations will hardly ever fail irrespective of their quality, because they'll receive universal acclaim from the media (which many people take to be objective fact for some reason) and like-minded people will congregate on the internet to create the illusion of a majority opinion, and that will be that. Sales will also support this, with sales being the only measurement of success that companies care about. Despite the polarising nature of Sword and Shield they're still the best selling Pokemon titles in years, which completely sweeps away will criticism as far as TPC is concerned.
I'd agree with you that Kingdom Hearts is unique in a sense - at least the earlier titles, which blended Final Fantasy and Disney quite well; the latter ones moved away from that entirely and became more their own thing from a narrative/character standpoint - but Pokemon is by no means unique, it's just the most recognisable and longest-running monster capture franchise. It wasn't even the first series to incorporate the idea, Dragon Quest was a few years earlier. There are plenty of series you could look at if you wanted to play something with monster raising gameplay, although they would mostly have a slightly different take on them. Kingdom Hearts you might be more hard-pressed to find something with a similar sort of vibe, but ARPGs are a dime a dozen these days, so you won't find the market lacking in terms of gameplay. Really, it'd depend on what you're looking for...and again, if you're looking for similar gameplay experiences, going in without expecting it to be exactly the same or very similar would only make your chances of enjoying it that much greater. Most people use "clone" as a derogatory term, but no one franchise owns an idea or gameplay mechanic. Nothing is really "unique" in that sense, because you can find other games that do almost exactly the same thing - this is why we have genres, after all.
