Well lets be honest here, if you want a "Game" like what you described, you go play Civ. or DoW (not the shitty 3rd one though), etc.
Most of these games are ment to be super casual where you are not required to actually "play". You set up your team and let the auto combat do its thing. No one can expect Xcom when coming into these games. Thats not what Browser games of this type set out to do.

Personally I would like to see some variety in AB. Heck they could even to few Tower Defense maps, where you deploy your tanks on a winding path, they dont move, lets say they are elevated or something, and the enemy sends enemies towards you general.
Or maybe a map where you can employ only Light tanks, and have to rush enemy positions. The map would be twice the size in length, and you would have to send your troops charging. Another one could be a hold the line mission where you can use only Heavy and Artillery tanks, and the enemy would send non tank units - Monsters (some reskinned creatures), at you and you would have to hold the line. offensive general abilities would be turned of and you could use only Heal and Defense up for example.
I mean there are options. Something to break the monotone line combat just like you mentioned.
But I suppose thats not what AB set out to do, I guess. Its supposed to be farily simple mobile game in the first place, so I do get it that improving on its aspects must be compatible with the mobile version, and they might be reluctant to change the formula that is already working.

I like the idea of Being able to upgrade tiles to some degree and assign tanks that could "work" the tile would be a interesting concept so that you bench sitting units have something to do.
It could for example give you things like placeable neko turrets, bunkers, mines etc. Just like what the enemy corruption gets, you could place some "annoyance" structures and items on the field before the start of the battle. The workable tiles would create these items - Imagine something like a hybrid between Factory and scouting, where multiple girls would be creating the item for a certain amount of time. It might cost some resources, and depending of how many girls and of what rarity are working on it, the building time might be reduced, or you would get a higher chance of getting better item (lets say there would be a 10% chance to get the big bunker Tower instead of the small neko turret, or something of that sorts")
Yeah those would some cool things to break the boring monotone feel of the game, even if a little bit.
PoC is another thing by itself though, but... ah well.