Wow, that’s a big difference from one side to the other! I’m not sure what to say, it’s hard to rotate a sponge cake without it falling. Might be worth trying it without the strips if they weren’t covering part of the pan- when I use strips on a springform, I use one (homemade) large enough to cover everything.
If the problem is severe hot/cold areas of the oven, you could try lining it with ceramic tiles to help even out the heat.
Since this is a sponge cake, small changes in pan size aren’t as important as they are with a butter cake, I think you can probably pick any reasonable pan that will fit all the batter (or scale the recipe up or down).