The only reason Pac is up around welterweight is Oscar.

Oscar wanted to end his career on a high by beating the P4P no.1, the Mexicutioner. Pac didn't care about the weight disadvantage because of the filthy lucre on offer. Obviously it backfired on Oscar and a whole new load of lovely huge money options were opened up for Pac.

Pac would have needed around 4-5 fights below 140 to match what he earned against Hatton alone. And remember he weighed as low as 138 for Hatton, so i'm sure he could have done it. Although only a mental would have gone back to where the money wasn't.