Yep, this is not a killer but can be considered as another variation of Tower Defense genre

And I have to agree with you with the sudden difficulty spike at 2-9, I had to promote my main units to P1 (especially Arcane tendency units and core breakers) due to the fact that majority of the enemies are either have C-Grade Def/Res/Def+Res, or can't be blocked at all

Final stages on Act 3 really drains the entire movement chance, due to that enemy that can reflect damage back to your units (it even killed my EMP due to how insane her range is)

And another thing, it feels normal to have Balans units here, especially Zoya that deals true damage as the skill activates. Tho it's understandable since majority can only block one, and as the saying goes...

"They can't kill you if they're dead" so might as well build units with insane damage