Agreed on all 3 points, particularly your first on their commander focus. I’ve never considered the color pie corruption via Commander too but that makes a ton of sense.

I think when they started printing directly to Commander—as opposed to letting cards printed for standard sets trickle down naturally to Commander–they introduced immense issues to both Commander and regular formats. It’s a format designed for 4 players and an eternal one that they need to now “rotate” with increasingly powerful cards. Not only does this corrupt the spirit of Commander (finding new uses for cards that never got played elsewhere), it cannot work with 2-player constructed formats and has caused a ton of issues there.

I just wish they’d go back to only designing cards for Standard and limited, and let the eternal formats (Commander included) get them naturally. Sadly it just is never going to happen, it’s too big a cash cow.

I think your question would make a really good post of it’s own, but my best suggestion would be to write down the mana curve you want first and build your deck to fit cards into that curve. Say you want 10 1cc spells, 20 2cc spells, 25 3cc spells, and 10 4+cc spells with 35 lands. There are so many possible cards you can include in your commander deck that I think it’s better to choose them based on a structured mana curve you want. That way your deck won’t fall apart while you play it, and you have a clear system for how to swap/upgrade/replace cards in your deck.

This doesn’t directly answer your question on paring the big pool down, but I bookmarked this a while ago that had a pretty good overview of EDH deckbuilding basics that might help, including numbers on how many of each category to go with: https://www.archidekt.com/decks/1048638#EDH__Deck_Template_(read_description_at_bottom) (and original source). It links to a separate guide on lands too which is helpful.

In general I think it’s really helpful to set a goal at the beginning. Are you building a deck to primarily have fun and/or explore a theme, do you want to try to be competitive, etc. I tend to choose the cards that I enjoy playing over those that might be “strictly better,” for instance, particularly ones that I have nostalgia for. I also tend to build around themes/tribes a lot which naturally limits the pool.

I agree with mike that this could be a whole post on its own, but something that’s helped me pare down the pile of potentials was the rough guidelines that both Prof (TCC) and Tomer (Goldfish) put out a couple of years ago, where they talk about how much ramp vs removal vs card draw you should aim for (I still try to run at least one “you win the game” card in every deck, in line with Tomer’s suggestion).

I still review my 99 with that in mind, even if I don’t always hit those exact numbers, and it’s helped make my decks play more smoothly whenever I run them, and is also really helpful when upgrading, since I know if I’m adding a new card draw engine, then my cuts should be from my existing card draw.