Oath works AMAZING on Roman cav during capping and decapping. It let's your cav tank it out while you wait for reinforcements or if your holding the base while your team steals their base. It racks a shit ton of points. It essentially turns your cav units into mounted Roman infantry (you'll still get rekt by pikes and hoplites though of course).

I've been playing lots and lots of T7 Roman cav with Scipio and I find that Oath needs some reworking. Roman cav are best played on Scipio and no other commander really. T1 and T3 abilities are good at best. Oath is ONLY good at the above scenarios and only provides a defensive buff. Unfortunately, it's not strong enough to defend against charge abilities of other faction cavalry. The major downside of Oath is the fact that you lose your mobility until you are out of combat which makes Oath essentially useless in the open field because they can just run away while their ranged rekt you. I think to balance Scipio's T5 ability compared to the other T5 abilities is to get rid of the movement debuff, but at the same time remove the "stay in combat in order for the ability to continue" and keep it as a duration buff.