Much of the time I have a web browser using a whole portrait-aligned monitor, but sometimes I feel like having it 2-up in a landscape monitor.
The win of nice clean window separation, without giving up significant percentage of my display space to window decoration, is -profound-.
I have one pixel borders around my shells, and I have it because I fiddled with zero and decided I liked one better. How many pixels do you lose to decoration, so you can mouse over them cleanly? That's a major win.
What does this have to do with a tiling window manager? I'd expect the app decides how to display window decoration, not the window manager. In fact I can confirm that right now since Chrome has different window decoration than say TextEdit. Also, scrollbars, macOS has them invisible by default so they don't take any space.
As for 2-up. Both Windows and Mac have shortcuts for that case
Plus thumbs at the corners, for some displays.
When I do, I either keep the fullscreen browser on a dedicated desktop or nudge the split point until I'm happy.
This, I can't imagine anyone wanting that sort of tiling. Anytime I have a use case for tiling in my own job it ends up being impossible to get things tiled the way I want and also have the things I don't want tiled setup correctly on my other screen.