This is a Gnome oddity that I dislike as well. I think it's considered a "feature" which I'll call application stacking. Hitting Alt-TAB brings up the terminal showing both terminals and you have to click the one you want to get to it. Quite annoying (at least for me). I got around this in 18.04 by installing Unity which defaults to the behaviour you and I seem to expect/desire.
This process is very easy.
- Enable the Universe repository
- Install Unity
sudo apt install unity
- Select Unity from the Gear Icon prior to login. (You can always go back to gnome via the same icon if desired)
Note that installing unity will install a rather large number of packages (~59)required to support it. However if having the system work as you desire is worth the space (~30MB) it takes for you it's well worth it.
Another alternative possibility is the use of extensions shuch as Coverflow or AlternateTab However I have not tested those as of this writing.
You could also customize the keybindings as discussed here.
As far as the display manager hanging you might find this Q&A useful.