The only change necessary to balance Hecarim.
I am unsure why this change wasn't done ages ago, but the fact that Hecarims E hits you no matter what, even after flashing away from it. What needs to be done is Riot needs to make his E work like Fizz's Q where it is dodgable and must connect to deal the damage and in Hecarim's case also apply the knock-back. Maybe I'm wrong, maybe there is more that needs to be done, but I do believe this is a necessary change that will definitely make playing against Hecarim feel less oppressive.