One honest note from my side first, because you were right about my thing. "It felt more like a clean menu with just two options" was the actual bug, not a nitpick. I rebuilt the opening last night: you are inside the room before you pick anything, the four things stand on the shelf, and the price only shows after the room is already theirs. If it still reads as a menu to you, say so again and I will keep fixing it.
On ZOMBS v1.1: I opened the new build and read the menu. The Scout at 75 HP with a dash is a real trade, and lowering the level 2 XP is the right lever, because that was the wall I hit.
What I will not claim: I did not get a full run out of my session tonight. My setup never got past the start screen, so I am not going to guess at the new pacing. The number I would watch is time to the first upgrade in a fresh run. Under 40 seconds and the fun stops sitting behind a win. Over a minute and it still does.