The understanding of an app quitting when the last window is closed is something that I go back and forth on if I like it or not. I think it really depends on the app. Launching Adobe apps take long enough that it is annoying to need to relaunch them, so I really appreciate that they don't quit on close of last window. Yet apps like Lightroom must totally relaunch just to switch to a new library which is extremely frustrating.

So it seems to me that Cmd-Tab is less of the offender to you than the app not behaving as you prefer when there are no active windows. Seems like your ire is slightly misdirected.