It's honestly kind of annoying that I have to spend a lot on factories to use T3 land/air to fend off a massive T1 land/air/sea spam from an enemy phantom... then he shows up with a GC in my base.
Why should any T3 grant you access simultaneously to air, land AND sea XPs?
You want Air XP? Get a T3 air hq. Sea? Get T3 sea HQ. Land? T3 land HQ. You want the game ender? well who cares about that one, nobody builds them anyways lol