I have to say, I disagree with both of these fairly fundamentally, and I think that all of the downsides of both of these things have been circumvented in more modern games.
1. I really disagree that there are too many types in Pokémon, and I think that there should only be more. Yes there's a lot of discussion on content bloat recently and potentially over-complicating gameplay, but this is only really an issue for young or intensely casual players who only play through the main games -- and now, once you fight a Pokémon once you're told what moves will be effective against it in-battle. This means that you don't even need to memorise the type chart never mind what type each Pokémon is, because the game lets you cheat anyway. All in all, it means that having type bloat doesn't affect gameplay for casual players, which is the only group it could negatively affect.
I think having loads of types is the foundation of competitive play, honestly. We still have a lot of Pokémon whose niches derive primarily from their types themselves, because every metagame has one or two type combinations that manage to stonewall the top threats. Quagsire and Gastrodon, for example, have been viable in OU since their introduction because Water/Ground always ends up being an amazing anti-meta type combination (with reliable recovery), and the same isn't true for Water/Rock. This demonstrates that you can't just merge the types together and expect everything to be exactly the same competitively -- even similar types on single-typed Pokémon can be wildly different once they become combined with other types. Furthermore, types are the fundamental of a Pokémon's identity: even superficially, were we to merge Water/Ice it removes the distinction between a polar water dweller like Walrein and an equatorial one like Octillery. These two Pokémon could never exist in the same ecosystem, ecosystems being roughly what Pokémon types fulfil the purpose of organising, so it would be odd to see them treated exactly the same. The small changes in how types work may not be too important in-game, but they make or break Pokémon competitively, and they add a lot of worldbuilding. Fairy-Type is an example of a new type being introduced seamlessly and enriching the worldbuilding of the series, so I think we need more types, not less (gradually introduced).
2. I don't think not being able to give every Pokémon "enough" attention is a valid reason to stop introducing new Pokémon. Since the very first game, each generation comes with a few iconic Pokémon and the rest of them the player gets to choose whether they like, love or hate them. The player gives attention to their top 6 by including those Pokémon on their team and beating the Champion with them. If they really love the world of Pokémon, they can play through the game again with 6 more Pokémon and develop bonds with them, too! I find this line of argument faulty because the reason why people are annoyed at Pokémon not receiving enough attention is because the designs are so good to start with, meaning they deserve that attention. But if the Pokémon are already good enough to deserve attention without being put under a spotlight, then they don't actually need to be showcased especially to begin with. It's just part of being a fan of a series with as many characters and assets as Pokémon has: I'm sure when Harry Potter was being released there were people out there begging for Mafalda Hopkirk to receive a sub-plot, and people have been requesting Waluigi to appear in a platformer for decades too. The fact that they're not getting special treatment doesn't mean that they shouldn't have existed either, nor that the series should stop introducing new characters to pay off those characters' debts. They're popular enough already, so it doesn't make sense to do it.
That said, Gen VI and to an extent Gen VIII have both done what you're requesting, albeit to a fairly shallow degree. Megas and Gigantamax both clearly seem to be a way of giving old favourites and forgotten-abouts new life. Yes they give forms to Charizard, Mewtwo and Gengar because they're old classics that warm people up to the mechanic, but then they hit you out of left field with Banette, Mawile, Sableye, Garbodor, Audino, Butterfree, Lopunny, Glalie, and others -- Pokémon that had dropped off of many people's radars but caught a second wind through these mechanics that for the most part has actually persisted. There's a way to give old Pokémon spotlights while still introducing new Pokémon and it's one of the things that Gen VI especially did right with megas, and there's potential for more mechanics like this in the future (or just a new batch of megas, perhaps replacing the old ones).
