Thanks for the reply!
I hadn't given the booster buildings a try because I haven't had the room in my city up until recently. I may try them out in the next week or two. This weeks spire was the perfect representation of my point though. I'm screwed on the 6th fight in. I pit light melee and light ranged, both of which have complete advantage/parity over the opposing force, with squad sizes of 86 on my end to 96 on the Spires (2nd city, chapter 3). Every other fight I've ever taken at that ratio, with that advantage balance, I would win, no booster building needed. This time, both fights were sound defeats.
The terrain is an interesting point. You're comment is the first hint I've seen about it, anywhere. The game itself never mentions it as a factor, from what I've seen (including in the combat help menu that I just checked to see if I missed it), so if it is that important of a factor, I'm very frustrated with them for not communicating it as a mechanic. If it's that influential on a core game mechanic, there is no excuse for not communicating it to players.
To be honest, I haven't really had a problem keeping enough soldiers recruited to field a full 5 squads of any of the unit types, yet, even with them getting wiped out regularly. I tried catering the spire one time and found it also severely lacking in communication as to how that works. For me it was just a guessing game as to what resource was needed where, which make that process far more expensive than throwing away units.
From what you've said, I'm inferring that there is a lot more nuance to these mechanics than they've communicated which enables people who know about them to be able to deal with them easily. But for the rest of us, who aren't in the know, it's just an incredibly frustrating experience. I've now reached the point where I don't plan on interacting with the Spire at all, beyond possibly the first four fights. For me, it's a just a waste of time, resources and frustration.