I feel like FRPs add more to the game than they take away. Setting one up can leave you vulnerable if you retreat many forces at once, and they're easy targets for artillery too. Ever try throwing a nade right on the FRP when OKW tries retreating to defend it?
I'd far rather that FRPs were added in for every army than for them to disappear entirely. An OH bunker upgrade makes sense, and as for SU... maybe an ambient building upgrade that isn't FHQ?