Fantastic rundown, mate. A lot of these mechanics I only vaguely understood. The evidence chests, for example.
Betrayal was a bust, for me. It felt very 'tacked on', particularly when you're deep in the Dread Thicket and come across a Syndicate fortification.
Einhar's menagerie/catching unique mobs was excellent, I actually enjoyed the challenge of using/managing nets directly, although I understand a heap of people hated it.
Niko's Azurite mine was also really engaging; flares, dynamite, darkness that hurts you.
Playing on the Xbox, I do struggle, with button allocations. You only have 8 buttons you can assign, so by the time you add nets or flares, you're often low on options for other skills/spells/attacks, so in that regard, the Betrayal League was simpler.
They could add the occasional caravan to the main game; that was a fun mechanic; but the conspiracy theory wall of strings was a bit full-on for my tastes.