It does actually hurt something --- my time. If the windows are on top of each other, that means I cannot see the one on the bottom. Which means I either have to click between 2 windows or make them tiled like you described (aka using a tiling WM but shit). Both options are inferior experience to a tiling WM which handles this automatically.
I don't think tiling WMs are some mega productivity boost. But I also think that floating WMs are just a worse workflow with almost no benefits. The only exception is if you want to see only a part of a window, which is easier to do on floating WM. But that's a rare situation and you can do it on a floating WM too, it just takes like 5 seconds more to set up.
Number 2 is an implementation issue. Dialogs should be floating by default.
Number 3 is funny to me, because that's exactly the experience I have when using a floating WM.