Seeing more than one at a time is high value.
I personally hate the basic tile schemes, and full screen in many of my use cases. Yes, when I'm using one app hard, full screen is good.
When I'm using multiple ones, I often want to copy paste info, or just refer to it. Auto pop to foreground is toxic, it forces a change in state when there is no need for that change most of the time.
On IRIX, focus follows mouse, and middle button copy paste were awesome. Still prefer that over other schemes.
Many people get a second screen to accomplish what can very easily be done with one a lot of the time.
Tablets are fine consumption devices. Some create is there, like graphics, but most create has UX requirements that exceed the simple touch sweet spots.