I wouldn’t rule out barbell work or split squats. Barbell work is very useful, probably essential, for max strength work. Split squats are great for both max strength and LME, albeit with different loads.
WRT lunge types, I don’t have enough experience to say. They all seem similar enough that perhaps it’s splitting hairs to recommend one type over another.
I do like the idea of reverse negative lunges. That seems like a great way to overload the upward-locomotive muscle groups which would be pretty specific to alpine travel. (Caveat: …but I haven’t tried them.)