Another potential solution that came to mind is increasing the number of units that can be garrisoned inside a fortress. Isn’t 20 soldiers too few for a fortress? Historically, 20 soldiers is already a very small number, it feels the same in game as well. A temple can hold 20 soldiers too. A fortress and a temple having the same capacity doesn’t feel right, maybe this could be adjusted. (It’s also interesting that theaters, which historically hosted performances for thousands of people in ancient times, can only hold 5 units.)

I expected (before knowing about capture mathematics) that capture points of garrisoned units value with a bonus factor.  Defenders with fortification fight from advantageous ground so one soldier is of higher value. This would be one option to strongen Buildings. Another possiblility would be to give a malus depending on the amount of attackers. So that capture points can not be massed the way it is possible now. Like the slower building process with more simultaneous workers. (Just my 2 cent....; but yes at the moment 0ad is an attackers game)

Not the cleanest game, but Zagros Mountains is really a good map for these skirmishes. Population cap set to 200, to avoid massive lags in late game.   Mace_VS_Rome_H.zip

totally, there needs to be some pushing. Or just remove the option that stops formations from being disbanded as it is pretty much only useful for the exploit.

There are quite a few ways to do this but ideally first fix the limitations that this behavior tries to compensate for.. +8 is generally elevation bonus to range, aka the height of the turret itself. If you look into the selection tooltip it will show you total elevation bonus, which include how high on terrain the tower is (on a hill for example), however I found out recently that this wasn't correctly applied (see proposed fix for it). With arrow shooter tech it become 60base +8tech +9elevation total bonus (IIRC vanilla show them merged so +17). Stone towers also have higher base elevation bonus..