I whole heartedly agree that adding the Containment Priest helps a lot with the Dredge match up and it adds a body to a deck that is slow to get bodies on the board. It also helps against Oath but not as much as it does against Dredge. The Containment Priest hurts you in the mirror and is often an unwelcome card to see when you facing another Xerox deck since it is a creature that does not add any advantage.
All that being said, I'm with Brian that I hate this deck and wish it would just fall off of a cliff and die. The conditions to beat this deck are just too situational.
I tested against it last night with Oath and I just pushed for an early Oath each game and keep pushing. They lost to whichever creature I got off of the Oath. They really only win with a early beatdown against you if you do not resolve an Oath.
I played Paradoxical which was even more annoying, and it is a waiting game. The deck has disruptive counter magic but either Erayo or pushing hard into Vault/Key is enough to steal games. It is not an easy match up but a winnable one.