Galaxy gunships and drop pods as well as other side grades.

[IMMentat]

Once they pin you inside, you cannot get out anymore as you cannot bring AA out that suffices. That is not good game design.

I fully agree about this.
The best thing the devs could have done or do is place access in the bases leading to under the wall turrets that you could, repair re-arm and possibly even control them from. Entry only through a hackable door deep within the base.
That said PS2 has far more 3D bases so turret and entrance positioning could allow for much better troop AV and AA defences.

PS1 bases operated like medieval castles, 1st true defence was turrets and vehicle patrols, 2nd was mines and chokepoints around courtyard entrances, 3rd yet more mines within an infantry killzone (courtyard), 4th was the main base entrances, and finally the stairwells then the choke-points around the spawns and Control Console.

The external battle was only half the war in a pitched fight, the NTU silo forcing a much needed timer on each base defence tended to mean that attackers had the advantage in a lengthly engagement (until the side that got pinned in resupplied with vehicles and came back to return the favour).