Really, really needs across the board upgrade cost reduction. When it takes multiple repetitive runs to upgrade one building one early stage, that's a problem. I would recommend outright halving the cost of upgrades or more. This game really doesn't have the intricate combat of Darkest Dungeon, and to then take far longer for less significant upgrades? Not great.
This grinding issue is further exacerbated by the style of the map and inability to rerun areas; while I do like how it incentivizes reckless behavior (via prioritizing clearing higher difficulty stuff if it would eat the same squares as lower difficulty), it does also mean that losing/crippling a squad could have permanent consequences. Contrast with Darkest Dungeon, where losing a squad hurt but you could always redo low-level dungeons until they were back up to a reasonable level. As a stopgap, perhaps an option to reset the map so that people could keep their town upgrades without needing to restart the game altogether if they end up stuck?
The grinding is my primary complaint, though. It really is egregious.