The 4-3 doesn't suck, the undersized Tampa 2 4-3 sucks! The Bills could have probably saved themselves an extra year of rebuilding by sticking with the 4-3 and replacing a couple of players instead of switching to the 3-4 and then turning 3 of your DE's into OLB'ers(ask GB how that worked out with Kampman), creating a position(NT) which you had absolutely no players on the roster to fill that spot, along with the DE position which at the time the switch was announced, you had one former DT moved to DE.
So by switching to the 3-4, you created holes at both OLB, NT and DE, not to mention depth at these positions.