I run a full clone team (Rex, Echo, Fives, Sarge and a variable +1) and sarge isn't a bad option in a non-clone team when appropriately geared up but there's a lot better. However, in a full clone team...his survivability and dmg increase significantly.
I have him gear 8, level 60, and 5*...he punches well above his weight when on a clone sqd. I've been pleasantly surprised with his performance. The AOE attack becomes very useful when ranked up do to the ability to cut enemy TM down significantly.