Petit is not the best big mountain skier. Best big mountain/backcountry combination skier, maybe, but best big mountain skier, not yet. He needs to put down lines like Seth, Sage, Hoji, before he is on that level.
Sage, Seth, Daron Rahlves, Hoji, Candide......There are lots of names that can be on this list.
I would add Richard Permin. He is one of the few guys who actually kills big mountain, and park. He has competed on the FWT, which says a whole lot. Watch The Way I See It, and you can see him ski big mountain lines with the likes of Kay Zackrisson, which many of the all-arounders, Sammy C for example, cannot do. In this years movie he was more featured, and just destroyed it. I don't know if anyone out there can ski big lines and dominate park jumps the way Permin does. He is someone who could have a career in either discipline. There aren't many guys like that.
Daron Rahlves is one of the best racers ever. He is also one of the best big mountain skiers on the planet. That might qualify him as the best skier to walk the planet.