I ended up using Moom [1] to work around some of the oddities of macOS window management. It's relatively low-feature, mostly for window arrangements and sizing. I use it on a vertical monitor to split window placement horizontally, since macOS can only natively do vertical splits.
It has other features too (like saving layouts and keyboard shortcuts), but I don't use them that much.
It has other features too (like saving layouts and keyboard shortcuts), but I don't use them that much.
1. https://manytricks.com/moom/