Mings and Konsa did a fine job last season defensively, didn't concede many goals bar a couple games under Emery.
But the fact we are even in for Torres despite having two good defenders means Emery wants more than just CBs who defend well. He wants them to have the passing ability to start attacks. Mings and Konsa simply don't have that in their locker, Konsa especially, Mings has to a degree, but nowhere near the level of Torres.