Lucas can't win it, not alone. There are too many times where you will face a Marth, Snake, or MK in large tournies. Sure you'll be able to overcome some of them. You'll get a few surprise wins here and there, but nothing that's gonna take you to Grand Finals.
What people need to understand is that when you discuss a MU and come to a ratio of 30:70, that means that at THE HIGHEST LEVEL OF PLAY (we're talking like Ally's Snake and a Lucas Main as good as Ally) the lucas only stands a 30% chance of winning. No matter how good the Lucas main is, it's still d*mn hard to win, h*ll near impossible to win.
So what do we do about this? Well, pick up a solid secondary or two to cover your bad MU's and hope you don't get CP'd. My personal suggestion would be Lucas, Snake, D3. OR Lucas, Snake, MK. But this means that you're not really using Lucas to win the big tourney. Just because you win a few matches here and there with Lucas doesn't mean Lucas is winning the big tourney... you'll be winning the MAJORITY of the matches with your secondaries.
IMO, we don't main Lucas to win. We main Lucas to have fun, and when we win a set with him, it feels great to overcome the odds and prove your skill with a low tier character. We get recognition, which everybody loves. You can't deny that you love when you use Lucas at a tourney, do a zap jump, or dtilt lock and after the match people say you're the best Lucas they've ever seen. If you mained MK, Snake, or any other top tier character, I can assure you that people won't be saying that stuff about you. There's just far too many people that main them, and because of these reasons, we stick to Lucas, because we love the challenge, love winning with him, and love when the people meat ride us about it afterwards.