I loved BetterSnapTool, but I'm glad my workflow has simplified to the point where allowing my windows to be subjected to the tyranny of a dynamic tiling window manager actually made sense, and now I feel more at home than ever!
I used Magnet before Big Sur, but have actually since switched to using Stage Manager. With multiple screens, I find that I seldom need more than two active apps simultaneously, and it actually helps me manage my focus better.
Yeah, I thought so too, but I find the exact configuration of which windows I want open and how big I want each one does change a lot.
It really depends on the size and resolution of your screens and use case. If you're using wide, high resolution screens, I really want to be able to place multiple windows in different arrangements on one screen for app development.
I find myself constantly shuffling windows around on my setup.