Hacker News Reader

I use a rMBP 2016 with one additional monitor over Thunderbolt to HDMI. I constantly have the same issue as OP.

Shouldn't you, though? Display arrangement lets you relocate the menu bar—imo that's as good a signal as any about which monitor should be the default.

Do you have "Displays have separate spaces" unchecked in mission control settings?

Click on one monitor and then move mouse to another monitor and move mouse down to the edge (without clicking anywhere). Of all alien, obscure and mind bogingly bizzare ux behaviors this would be probably in my top 5.

I would hope that my dock would be on whichever screen my mouse is, so I don't have to drag my mouse across a large monitor to get way over there to get to the trash.

What you term "alien, obscure, and mind-bogglingly bizarre" is the only way I think should work.