So update, after about another hour of attempts I managed to do it! I can't even imagine how long it would be if I also had to do those mechs again before each of those attempts! The boss is still insanely hard on Veteran, so the challenge is still very much there which is great! It's now just a lot more manageable haha

btw, for anyone else stuck on that last boss with this update you will need to copy your old save file into the new Trenchpunk folder from within your users/<username>/appdata/Roaming/Trenchpunk (I now had two save folders there after booting the new version, one old and one new one)