If the team were going to be any good in the next 3-4 years I would agree, what I question is what the team would accomplish during the contract and what the cap limitations would be ie. who might have to go due to cap limits while he was here.
I suppose he could always be moved if it's clear we are going to miss his window in the last few years. The nightmare scenario would be that he declines to unmoveable status (ie Phaneuf if he doesn't turn it around, Lecavalier, many others) and then we're handcuffed with big cap. Tampa got a (cap-)free buyout on Lecavalier a luxury that won't be available in the future.
Still if he's willing to sign here you almost have to do it because of how hard it is to land that kind of talent outside the draft without giving up assets...