I think that several of them could have won it. Virgil was strong, but he did not seem to be that strong to me. He looked to be very beatable. Tyson and Tobias would (not could, would) definitely have won the Unova League. I'd also put Gary, Paul, and Harrison into that category as well. Even Conway could have made it far and may have been able to beat Virgil. The crop of Unova League participants did not seem to be anything special so Virgil winning it does not seem as impressive as some of the other champions winning their leagues. Heck, OI, Johto (with Kanto Pokémon), AG, and Sinnoh Ash could have won Unova just as easily as any of the rivals I just mentioned.