Forts? How?

[WinsingtonIII]

but the AI are too stupid to just kill the fort with just 20-ish pandas inside, they merely stop at the edge, and don't even try to besiege that

Yeah it's definitely true, free forts can save your butt as Pontos in the early game. If you place some strategically before you go into debt (with one panda in each) then the AS can never launch surprise sieges on your capital (and if you do it right, Ankyra as well) because they will attack the forts first.

Pantodapoi are one of the worst units in the game. They die like flies to arrows.

As Cute Wolf said, it's not the battle map value of them but the strategic map value. Even with only one unit of them in a fort you create a diversion for the AS to screw around with instead of besieging your capital. With a whole stack of them, as Cute Wolf mentioned, you can prevent them from attacking from that direction entirely unless they bring a full stack of their own. The AI doesn't seem to distinguish the quality of troops in a stack when deciding whether they have the advantage to attack, just the number.