I've tried quite a few different launchers now and I've only found one so far that handles landscape mode well. (TL;DR, it's Total Launcher).
The Pro1 default Quickstep supports landscape mode but only using a "two halves" approach that screws up widget placement (my old 1x1 and 2x1 widgets all get stretched to 2 rows, and can't be positioned across the center line of the screen), and it also lacks a lot of other pretty basic customization options.
Some launchers don't support landscape mode at all, they're just in portrait mode all the time. These include: Evie and Smart Launcher (n