I think actual stats are fine if the stone is considered for tanks, not for grinding. Hp regen is obvious and speed for those groups that rush from mobs to mobs not waiting for tank so he gets some more speed in those moments. Also tank without ranged taunt has more speed in combat and he needs it imo.
PC EU (PL): 14 characters. ESO player since 06.08.2015. Farkas finest quote: "Some people don't think I'm smart. Those people get my fist. But you, I like."
You should've also mentioned that the Steed also adds HP regen. Right now, you're making it sound it ONLY increases run speed. If that is case (in case my source is incorrect), then sure, change it to movement speed.