Never! While I do manage to get through the games, I'm usually struggling at one point or another, since I'm horrible at managing my teams. The levels are usually greatly varied, up untill the point where I either need one of the underleveled Pokemon a lot, or I just decide to even out the levels, I'm not really great at choosing suitable movesets, and usually just end up going for the strongest moves, unless I already have something that works well enough.
I just think doing a solo run would include too much grinding for me, and I'd really have to think over what moves to use, and I'm not really knowledgable in that respect. I did manage to get to the Elite 4 in Leafgreen using only my Venusaur and Clefable, but that wasn't exactly easy, and I never got any further, so I was still quite the way from completing the game. I can't imagine doing all that with one Pokemon, so I doubt I'd ever succeed if I actually tried doing a solo run :/
Short answer: No