What really matters when developing something isn't the time or budget in itself, but what the team does with that time and budget. Pokémon Red and Green were developed in six years and still turned out to be pretty buggy games with lots of design oversights (the Japanese Red and Green is more buggy than the international versions).
And then there's Cyberpunk 2077...
Also
Sonic Forces, which took four years in development. A breakdown of it, however, indicates long-term planning, as three of those years were made building the engine for the game while approximately 9 months was made for making the game, which explains why it feels incomplete and the story reading like a first or second draft. For comparison, the only Nintendo project known to have a development cycle of several months was
The Legend of Zelda: Majora's Mask, which was, of course, achieved by reusing assets from
Ocarina of Time and making a smaller world in Termina than Hyrule.
Pokémon Red/Blue/Green/Yellow came out as it was because it was made mostly by a small team from what would've been an indie studio at the time. (Game Freak is arguably still an indie studio now, albeit in the same category as Mojang and Toby Fox Productions due to having one breakout cultural phenomenon hit.) They didn't have the technical skill or manpower to make out something comparable to a triple-A production at the time. The production cycle mirrored that of other indie games today.
Freedom Planet 2 is now at roughly 7 years in development, for instance, and it'll be 8 years when it's finally released in 2022.
It's probably less Game Freak (at best maybe Masuda) and more TPC. Game Freak likely does not have control over the budgets and release dates, it's probably set by some corporate executive in Pokemon's braintrust that knows nothing about how video games are actually made and is just setting them that way to maximize their bank accounts over making an actual quality game. This is honestly a much larger problem than Pokemon or even video games, this kind of business management has hurt a lot of aspects of society and there's a larger political/socioeconomic argument to be made here, but without derailing the thread with political arguments that are off topic Pokemon definitely seems to be a casualty of this style of business. You can feel it with how minimalist the recent games have been compared to some of the past ones.
Unfortunately, I think the only thing that can realistically fix this outside of larger political/economic changes that may or may not happen is Nintendo stepping in. Nintendo is one of the few companies that doesn't let the business side of things get in the way of quality gaming experiences (and even then that's not entirely true across the board, see: the NSO Expansion Pack being more than twice as expensive as the basic plan and offering very little to justify it), so they're the most likely entity involved in the Pokemon games to step in and say "No, spend more time on the games, we don't want you harming the reputation of our games with cheap, low quality games".
I want to point out that many Nintendo fans suspect SEGA is the reason behind NSO Expansion's jump in price (and there have been statements from SEGA to back it up, though I forget where I found it). SEGA refused to put games onto the Wii U's Virtual Console as they were dissatisfied with the money coming in from the Wii's Virtual Console; they wanted the prices to be higher on the Wii U but Nintendo refused, so they chose to avoid it entirely.
Not only would it make sense then for SEGA to ask for exorbitant amounts of money to put their games onto the Switch's Nintendo Switch Online service, but SEGA is a company that has been using the business model as you've described for far longer than The Pokémon Company has, as is evident in the Sonic franchise's many pitfalls due to their near absolute refusal to delay a game (the only known instance is the
Sonic Lost World which may have had Nintendo's influence) and the "lock-on technology" used for
Sonic 3 & Knuckles (the file size of
Sonic 3 and
Sonic & Knuckles combined could have fit into a cartridge of theirs, but because
Sonic 3 was running behind schedule, they released whatever was completed as
Sonic 3 with a minimalistic ending, then released the rest of it the following year as
Sonic & Knuckles).
I'm seeing very few explicit contradictions from the fanbase, it's been more of Fan A wants some feature and Fan B just doesn't care about that feature and ignores it. In that case, Fan B isn't really displeased if they include what Fan A wants and if they just include it both sides will still be happy with the end product. Including a large variety of content is the best way to please as much of the fanbase as possible, then there's something for everyone in the game and only a handful of fans (likely ones that are nitpicky about what they want out of a certain feature) go home unhappy.
I think some of it is and some of it isn't. The Battle Frontier is an example as you described: fans who don't care about the Battle Frontier won't care that it's there, and they'll just ignore it. Pokémon Contests too except where required to proceed.
Dynamax and Gigantamax, however, is not. The people who don't want Dynamax and Gigantamax are not happy it's in
Sword and Shield at all; some have refused to play them solely for that reason (and led up to Smogon's controversial Dynamax and Gigantamax ban, though my thoughts on that would belong elsewhere). On the other hand, now that
Brilliant Diamond and Shining Pearl have released without them, you're seeing the people who insist Dynamax and Gigantamax should've been in it. This divide with this mechanc has also brought out of the woodwork those who disliked Mega Evolution in Generations VI and VII, who had kept quiet during then because the fans happy about them had drowned them out.