While I agree supplementing with cycling or running is great, on the boulders if you’re too “top heavy” try focusing on “wobbly” problems more. Find a gym with a slab wall, and practice balance style climbing where you don’t need strength in the arms & shoulders. Doing that regularly will balance out the legs portion easily if biking or running isn’t your thing.
no it wont. Its not even remotely stimulating enough compared to actual lower body exercise.