In reply to dinodinosaur:
If you're struggling to keep your legs on then your core (not just abs) is the weak link, plus probably foot technique. Body positioning changes quite significantly on steep ground and one reason many people struggle is they attempt to apply the same principles as on slab/vertical/lightly overhanging terrain of keeping hips in, whereas with steep climbing that will quickly knacker the core and require much more force to keep the feet on. Instead, it's better to use a lot more twisting and drop knees to make longer moves, and focus on keeping the core tight when stretching out.
I am 78kg/173cm with muscular legs from a decade of mountain biking - I've always viewed it as positive as it means my joints are robust and well supported, I can work leg intensive positions such as hooks, bicycles and kneebars really well and I can drive loads of power through small footholds. I personally wouldn't recommend deliberately bulking legs up with squats but a strong base is very useful.