The problem is that a passion project is not necessarily one that will make a lot of money. Little Town Hero does come across as one, and possibly Giga Wrecker and Tembo too, but Pokémon aside, Game Freak is a small developer, and they make mostly indie-scale projects. That means they have to compromise on what they want to put in there, and what they want is not necessarily going to be well-liked.
What you describe is exactly what SEGA has been trying to do with Sonic for the past two decades. Each new Sonic game has a different gimmick to it, sometimes combining gimmicks from previous games that were well-received. Problem is that the Sonic fans are infamously fractured, demanding mutually opposing things. Some want more characters, and some want fewer characters. Some want more of the boost-type gameplay, while some want it done away with. Some want darker, more serious stories, but some want lighter, more comical ones. Some will not be satisfied until a game called Sonic Adventure 3 comes out, regardless of what it would be like. Some refuse to acknowledge Sonic's archnemesis as "Eggman" despite that being his name in Japan from the start.
The result is that it's impossible to make a Sonic game in which everything an "endless high note," because what some fans consider a high note, others consider a blemish.
You can see the same thing in Pokémon. Go outside of the fanbase and ask video gamers what they'd like in a Pokémon game, and you'll get a lot of people desiring for them to move away from turn-based battling. You'll get people who don't like any Pokémon past Generation I and want more of Pokémon Let's Go! Pikachu and Eevee. You'll get people who want a large minigame collection like they played in Pokémon Stadium and Pokémon Stadium 2 (and indeed, a lot of people picked up these games, ignoring the battling aspect and played it only as a minigame collection). Try proposing any of that here and it'd be treated as heresy.
That's the situation Game Freak has been in for a long time now. Pokémon is big enough, iconic enough, and most importantly, old enough that any decision they make is going to enrage some people.
Passion does not really have any correlation to profit, so I would half agree, but think it is a non-sequitur. What you were driving at with your last line (basically) is that Pokemon is a franchise and I think GF has been approaching it like that ever since R/S, probably in no small part because Nintendo is standing behind it's star child with two hands firmly on its shoulders. What I meant by passion project was to simply stop thinking about everything in terms of franchise economics and try to make the best game you can possibly make, and swing for the fences while you are doing so. This does not mean they have to throw anything out or do a 180 from where they are at, nor does it mean they have to forget that it is a series and will continue into the future (so do not gas yourselves in the attempt basically). They demonstrated with Sun and Moon that they will at least touch (if only aesthetically) the foundational elements of Pokemon, so it does not seem like too much of a stretch for GF to get together and distill the essence out of their stable of Pokemon games and universe, and then look at how they can make a phenomenal game drawing on the inspiration of the evolution of game design across the years, their own creativity, improvements in technology, and... well, passion, ha ha.
I make my language poetic for the sake of interpretation sometimes, and I honestly have written too many epic length forum posts only to have my soul crushed by indifference, so I have become accustomed to just rolling the dice with vaguer language to save myself a thorough explanation, ha ha. "Endless high note" was just meant to capture the feeling that the game should evoke, not necessarily a description of the litany of features it should have. You make a good point about how widely the opinions of fans, let alone just game players in general, can vary regarding feature lists for video games, and Sonic is a good example, although one I am not very personally familiar with, outside of tidbits I picked up reading Game Informer and good ol' Nintendo Power (rip) back in the day.
I do not think Pokemon is precisely in the same position however, because Sonic has been trying to re-invent itself (as far as I can tell) while Pokemon has been more liberal with its offshoots. Stadium, Let's Go, Mystery Dungeon, the weird free-to-play Cubivore rip off, etc. Pokemon is like a leviathan dragging a lot of detritus in its wake, but the core games have always had a pretty crystal clear focus. The stuff that has been thrown in and taken out has mostly been related to connectivity, until they introduced Mega-Evolution. I think as far as mainline games go, GF is in the clear to make the "best" version of those games because they have not iterated on them overmuch. That will change as they keep juggling around Mega Evos, Z-Moves, Dynamax, and on and on, but even those things are all just different flavors of an overpowered mode or move, which is a common video game trope. For most people, I would think, it would be easy to simply pick one and move on, if it would be conducive to the gameplay to keep them in at all. Maybe that would be one of the more difficult/unpopular decisions they'd be forced to make, but that is one of the few that strikes me off the top of my head.
The rest of the features they have had across games they could easily bring back and integrate, and then keep building the game, game play, features, and content. I think there is a strong illusion of developers being backed into corners in game critique and discussion, because we have all been so conditioned to not expect great things, but planned obsolescence has more to do with that than anything. And as I said, I would not expect them to give me EVERYTHING, because I know they need to plan for the future, but I think as they keep making games on a platform that hosts games of the scope and depth of Dragon Quest 11, BotW, and the Witcher, and ESPECIALLY because they are branching off into simpler mobile versions of their games to appeal to different players, they need to step their game up. I fully expect Sword and Shield to be transition games, but GF should be looking toward how to evolve their flagship games now that they have so many other avenues to work in.