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.
I'd add hiking or running to this. I've seen my coworkers get winded walking hilly sidewalks, any type of ambulatory work is at the heart of human function.
Plus rock climbing is fun and mentally challenging, like chess with your body.