you could say the same for all the Halo's. (I would have suggested using 5 for this because 5 does it the worst)

You really can't because Halo 1 - 3s story is contained and told within the games. It's only until Halo 4 that 343 uses the books as Canon Material to work off of leading to shit like. Well. Why the Elites are mean again (aside from the handwave early on), why the Didact is like that (other than being Lazy Evil), Lasky gets his backstory in the show...

I think I'd personally disagree, at least in part. I think the story collectively works with the understanding of needing to let go, move on with the passage of time to skies unfamiliar between Chief, Cortana, and Didact without any canon material or prior knowledge other than the first 3 games' general Chief-Cortana relationship. It's still an albeit messy one imo but I think that general theme and foil the Didact acts like for that is pretty straightforward.

Yeah I think halo 4's core story works well and all those lore tidbits I knew without the books. Maybe I looked up that the covenant you fight are just remnants and didnt get the memo from not the game, but I think Cortana says that in level 1? I think you learn Didact lore in the terminals? I don't even remember who Lasky is tbh.

Not sure if Im remembering all that correctly but I really don't think you need to read the books for this game. Like LunaEndlessWitch said, that personal story of the characters still works with the games before it and the other stuff that might need additional learning are (i think) less important and make sense to put in extraneous material.

Like I seriously think 5 (and Infinite) both do that with the main story and it fucking sucks. I really feel what you mean with those games instead. Like the story between 5 and Infinite really feels like they wanted to just fucking ignore it and move ahead because 5's sucks so bad. At least Infinite's story made sense character wise again.

PLEASE play umineko tho