And our beta testers will know that in AR, the Grizzly tank is very fast and, if used properly, can take down a full health / armour Apoc tank in 1 on 1 combat by simply dodging it's shots. Requires a lot of skill by the Grizzly driver, and relies on the Apoc driver not predicting their movement and leading the shot effectively (fast changes of direction help the Grizzly here).
Generally, between two equally skilled drivers, the Grizzly would lose, but the Apoc would take a heck of a beating first.
EDIT: And, of course, the Grizzly's driver can easily escape the ponderous Apoc tank, so if it looks like it is going to lose the battle it can just run away, while the Apoc, being a lot slower, would have a tough job escaping from a battle if the Grizzly driver wants to destroy it.
EDIT2: And don't forget, running away is a very good idea sometimes, since you will save your veterancy points that way. Getting killed strips all of your veterancy points from you, so should be avoided at all costs. Even if you don't kill the opponent you might still have a lot of points for damaging them, which all count towards your next promotion.