1 hit every 144 shots against a fully fortified GtO weapon... yeah, that doesn't sound really favourable while it's engaging you anyway. Maybe, maybe if you have shields do tank the blows, but certainly not on an armour paradigm.
Is there any degree of consistency in dominant terrain? I mean, dominant terrain is nice and easy, if not realistic, but do battles on the same planet always have the same terrain barring terraforming shenanigans? If it doesn't a lot of the plausibility disappears. I would've liked to see, say, 6 different 'dominant terrains' on an Earth sized land, but I understand that would get needlessly complex.
I'm curious however; does the existence of a biosphere impact the chances for certain terrains? Because it should, given so many imply a biosphere. And frankly, we need a way to measure the size of a biosphere, and to change biospheres if these are our options. Because to me? It looks like the best option, defensively speaking that is, is to jack up the temperature as far as the settling species can tolerate without infrastructure support and a hydrosphere as extensive as you can get without limiting maximum population to get as much chance of generating a Jungle terrain as possible.
Oh, and another dominant terrain type; Urban, for those planets at their maximum population without hydrosphere based population limitation.
And with high enough tectonic activity, hopefully mountain jungle terrain. Because that's where the best defense values are.