I find the instantaneous construction of terminals a bit strange.
It takes a single click to have a working terminal, meaning that airlines can surpass the gate limit at a moment's notice.
Normally, this is offset by making terminals very expensive, but airlines with deep pockets don't bat an eye.
What I suggest is simply making the construction of terminals take time rather than be instantaneous, the same way it takes time to build and deliver aircraft.
Even if it's just a few in-game days (or just a few hours in real-time), it'd feel much more reasonable having to wait for an entire terminal to be built rather than immediately being able to use it.
I know realism isn't exactly AE's forte, but this is less of a realism-based feature and more just common sense.
Maybe other people agree that this would be a good change?