What part of Diablo 4 is behind a microtransaction wall? Some skins?
I think it's "Most of the skins".
The problem with both games is they disrespect the player’s time by turning everything into a slog.
I can't speak for Diablo 4 on this, but that's not Starfield. Just like other Bethesda games, Starfield clearly gives feedback when you're leaving major storylines and running procedural content. Radiant Quests have mixed reception, but the number of radiant quests you actually need to complete any Bethesda game is in the single-digits.
If you stick to main-story and faction-mainline quests, you touch virtually nothing that wasn't hand-crafted for your pleasure. No slog. No grind. No nothing. And I find it pretty easy to differentiate between the handcrafted side-quests and the procedural side-quests. If you don't, just ignore the more obscure-seeming side quests anyway.
a boring 150+ hours of empty world with a total of 35 hours of interesting beats
Is this a personal self-discipline problem of yours? A game with 35 hours of great content is worth the price of a game like Starfield, and you can just NOT go out and play the "150+ hours of empty world" if you don't like it. While I haven't beaten Starfield yet (I like procedural content and spend a lot of time in it), that mainline content isn't gated behind doing procedural stuff. That stuff was added on top of the content you directly pay for.
For me, I love going system to system finding ships to pirate. I haven't really gotten into planetary exploration yet. Maybe I won't enjoy that as much, or maybe I will. If I don't enjoy it, I just won't do it and it won't detract from the game.