Same. I scrolled down to see if anyone beat the level or if it was just me. Seems like it's a dead end... I've also tried moving the towers around and I got pretty good results moving the ice wizard around incredibly quickly mid-game. In fact it was the farthest I've gotten doing that, though I still ended up dying anyways after 3 tries of this so ¯\_(ツ)_/¯.
Pro tip if you're doing this: freeze and cursor-attack the big guy as much as possible and ignore freezing the little guy. You'll end up freezing the little one in the process, but it's fast enough where it doesn't make much difference. Let your towers do damage on the little guy and concentrate mostly on slowing down and dwindling the health of the big one. The thing that worked for me is only one move: from the first section of the path to the second. Too much moving kills any time you have for cursor-attacks, so I found minimizing moving the towers as much as possible to be ideal.
I tried to move the other towers around mid-game but it seems to mess up the AI and cause them to stop shooting when I do. My worst runs were when I tried doing it with other towers. Sucks to see I can't just move my archers around because they do more damage than my cursor could ever do.
This is the furthest I've gotten btw:
