I never realized I was short on talent until I moved up to the Seattle area for a few years. I guess it was the crowd I hooked up with. My first ride up there, at Galbraith Mtn. in Bellingham was an eye opener. I was used to riding technical trails in Tucson and the Sierras but the slimy skinnies and big drops up there caught me off guard. I kept riding with the same group but was always off the back on the DH while I was usually one of the faster descenders with other groups.
A few thoughts regarding the cross training thing. I've had two lumbar surgeries as a result of being hit by a car while bike commuting. First surgery in 2001 and again in 2003. I have to take a more balanced approach to exercise than just riding or the sciatica symptoms come back. Singlespeeding is easier on me than spinning up hill but either way, if I just ride, I'll be in trouble within a month or two. Add a couple of days a week of strength training + stretching and I can ride all I want. Stretching alone helps some but isn't enough. I seem to need the balance from training opposing muscle groups to stay pain free.
I raced XC a lot between 1994-2006. Some of the better racers, mostly very skinny guys (duh), put up with a good deal of hip and shoulder girdle pain/discomfort doing long hours in the saddle. One of the local Tucson pros started a MTB training business and several of his clients managed to reduce or eliminate those issues with the core strengthening exercises he added to their training. My take away is that if your strength in some area is lacking, cross training can help. If it's not, then your riding won't benefit from it.