This is just really bad design for what is supposed to be a strategy RPG. What causes this is that the reinforcements in this level are triggered by you killing particular enemies, so if you kill the bulk of the starting enemy lineup in a single turn (like what happens here), this happens. It's a problem because it pushes the emphasis away from actual strategy and onto trial and error instead - instead of being given a situation that you can reasonably get out of with good preparation and strategy, the game just ****s a bunch of reinforcements on you, and expects you to keep retrying until you can figure out which enemy triggers which set of reinforcements.
I know other levels do this as well, but I think this is the worst example yet.
I'm only a little salty that this happened the first time I played the level and caused me to lose.
Still don't like when the game does something like this, and it's been getting a lot more frequent lately. Probably one of the main reasons why my interest in the game has been waning lately.