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..

Here's another idea. Capture attack -> Siege attack. Buildings can be captured only if they have less than 50% of total HP (some techs could bring this percent down further). Default action for units is now siege attack. Capture is possible as before, but only after a structure is below 50% of HP. Otherwise, the capture attack is disabled (has red X across the capture icon, to indicate it's disabled). Siege attack animation is the same as the capture animation, but units are holding the torches up instead of their weapons.