Look, Melnyk may be a huge pos but here's just the owner. Most of the time he's not even around. What happened in the dressing room and in his personal life had a lot more to do with Karlsson bring unhappy than anything Melnyk could have said or done.
I'm sure there are great owners out there as well as goodness asses like Melnyk. Look at what happened in Florida (when your GM gets denied like that it had to have come from the owner), Carolina, Montreal (Bergevin may have destroyed that team but the fact that he's still there makes me wonder how much of that is coming from Molson). At the end of the day, 11 of the 12 teams with higher payrolls didn't win the Cup, and a team near the bottom of that list came in second. They day Tampa has the best team and best chance to win? They've been saying that for thtee years. Would adding Karlsson put them over the top? Possibly, but there are no guarantees. It's say keeping Karlsson, Stone, Duchene and adding Tkachuk, White, Brown, Formenton could do the same for the Senators. Maybe not right away but in 2-3 years for sure.
Going to Tampa will give guarantee that he'll pay less in taxes, that's about it. The weather is only better during the winter, when he's busy being on the ice. Quality of life, otherwise, it's definitely better here.