I think Wallace is somewhat under rated here.
It seems like he is pretty good. Remember the Bills did not pressure the QB successfully this year and that impacts the back end.
This is not a bad player.
If McKenzie goes, and with John Brown gone, there isn't much speed on that offense. McKenzie made plays. He caught a touchdown in the AFC Championship game and had a 3 touchdown game. If McKittrick goes now you need two new guys, at least, who can pressure a defense with speed. That is the argument for keeping IM19.