I doubt if he would be happy with the Ruger in the long run if he buys it just because he shoots better with it. With experience he will improve. If he likes the Sig, he should get it, and with a little training and experience, he will improve.
I took a friend to the range and let her shoot a 1911 in 9mm. She was hitting the bottom of the target, and occasionally in the ground. In other words: she was flinching badly. Her husband had let her shoot his Kimber in 45ACP and she hated the recoil. My 1911 looked like his - mental problem. I then took a box of 357Mag, which was in a 38 Special box and let her shoot the Taurus 608. She is a far better shot than I.
When she was done shooting it, I told her to look at the brass. She was amazed to know that she was shooting a 357 Magnum. We went back to the 1911, and she was back in the dirt. I normally carry snap caps because I use them to test guns that I've worked on. (Load a snap-cap, then load a real round). I loaded 2 or 3 rounds, a snap cap, then a couple more rounds.
Bang, bang, dip. "Whoa, do you see what you did?" It was amazing - she corrected immediately. I realized that I was done shooting for the day because she was shooting much better than I could do.
She now loves shooting pistols, and I have to think back if I'd said to just shoot revolvers the fun she would be missing.
Incidentally, the best I've seen her shoot was with 45 ACP in the Sig 220 Sport. It is heavy, ported, and little muzzle flip. She knows now that I won't let her shoot anything that she can't handle. She liked the looks of my little Airlite revolver, but I wouldn't even let her shoot it with 38 Specials.
