Right. You need two good wingbacks to play a 3 CB system, Tolkin is fine on the left, but I dont think Edwards has the speed for a wingback role. And Harper doesnt look good enough defensively yet to rely on.
Straight up, I don't even like Tolkin at LWB. I really think that we would be better served using him and Edwards (or possibly now Duncan) as just regular fullbacks with Reyes and Long as the CB's. That is a top 3 backline in the league IMO.