Frazier is fine in general. His defense is usually good. I wouldn't mind him sticking around...with one caveat.
Against the best QBs, or in games where our 4 man rush isn't getting there, I would like the Head Coach to override the DC and implement the 3 or 5.
Show four, and then rush three. Everyone else drop. Or crowd the line for confusion (Rex Ryan style) and rush 3 or 5 from there. The games we lose is where we can't affect the QB with 4.