Why is it too much? We paid him 40 guaranteed as a rookie, and he's lived up to his draft billing. Is there something inherently unimportant about DTs? Do we realistically have better options to spend that money?
Suh makes our defense work. He draws double and triple teams inside that open up lanes for the rest of the line. Our DBs are still not that great, but they benefit from the pressure our line creates (which again is something Suh has a huge part in). Suh is the best defensive player on the team by a wide margin, and losing him would not be easy to replace at all, even with multiple players.
Because it's a DT. You could add other reasons, like With two others who are making mega contracts, Or the fact our CB's "are still not great" (your words), etc. So he's not easy to replace, upgrade elsewhere.
In the end I don't think it really matters. He seems to want to go elsewhere. Maybe lots of wins can change that. I doubt it but you never know.
I didn't know if they have the personal or can get it - to switch to the 3-4 but if both DT are gone it'll be easier in my opinion.