Wildlander's basically a full survival overhaul - it touches basically everything, including quest logic and pacing. You'll get constant friction with vanilla quests because the whole point is to make the game slower and harsher. Diplomatic Immunity still works, but you're dealing with hunger/fatigue/cold mechanics layered on top, which changes the feel pretty drastically. It's more of a "build your own Skyrim" fork than a "vanilla+ with teeth" mod.
Nolvus is actually closer to what you're asking for. It patches and rebalances without rewriting quest structure - you can run the Thieves Guild questline (the main one where you work with Delvin and Vex, then the bigger plot stuff) pretty much as intended, just with better combat AI and harder enemy scaling. The perks are tweaked but not replaced wholesale.
Honestly though, if you want vanilla quests to stay intact while adding difficulty, you might be better off just stacking individual mods - USSEP obviously, then something like Wildcat or a similar combat overhaul, maybe a perk mod like Ordinator if you want more build variety. That way you control what changes and what doesn't. Takes longer to set up in MO2 but you get exactly the experience you want instead of compromising on a preset.
What kind of difficulty are you after - just harder enemies, or also survival stuff like hunger/cold?
