I'm a self-checkout hater, but that's mostly because I'd rather dump my groceries on the conveyor and zone out while someone else gets paid to do the work. If I do self-checkout, I have to do everything myself and then it complains and I have to get staff to come fix it and it's all so stressful.

That one's a side-quest dungeon with a fixed layout. For the "By Three They Come" quest, judging by your quest journal.

The same way that the basements are 10 times bigger than the houses themselves.

I don't see how "make helltides almost completely pointless" could be a feature. But hey, it's Blizzard.

Sounds about right. If they've deliberately made this change, they should change the "recommended level" text on the world tier descriptions as it's now mandatory, not just recommended.

Finishing the campaign unlocks the campaign skip for new characters. Seasonal characters will not be able to access seasonal content (malignant hearts, extra story, etc) until the campaign is complete or skipped... so unless you feel like playing through the whole campaign again, you'll want to complete it with your eternal character first.

The massive drop rate reduction is a confirmed bug that they'll be hotfixing.

Still doing campaign at level 55? No wonder it's feeling grindy. Monsters cap out at level 50 in WT1/WT2 so you won't be getting much in the way of experience and you won't be getting better items.

Rerolling item affixes is done at the occultist (where you extract and inscribe aspects) and is called "enchanting". You unlock this at level 25.

it feels like work to dutifully collect all golds just to sell without even looking at them because i only care about legendary, which are rare and mostly not even useful for my build.

That's not quite right. Legendaries are usually only useful for their aspects. The rares are the ones you want to be looking at. You find a rare with 3/4 good affixes, reroll the last to something good, imprint a legendary aspect on it, and you've got an excellent item.

The dagger was comparing against your wand only, whereas the staff is 2-handed and compares against wand + offhand.

If you haven't done all the strongholds, there are a few in those.

Other than that, just run around the map to all the blurry bits and you'll find them. Or look up a map online.

The trick is... you don't get the mastery.

I found another I found in a cellar that seemed impossible - there's a guy trying to absorb some creatures or something (hey, I wasn't paying attention!), but they only seem to spawn one after every wave, and the guy has to do some long animation thing after you get the creature to 20% health or so. I only managed to get 2 of 5 done by the time the timer ran out. Maybe it'll be easier if I ever see this event again at a higher level, but I've only seen it once so far since release.