The unfortunate thing is when you are looking for specific match-up that specific information for match-ups require either a lot of experience playing on that champion and playing in those match-ups or playing on the other side of it for that one specific match-up. I have not played a lot of Hecarim and it's been far too long since I did. I'll try though.
A good thing to keep in mind since you are having trouble with Yasuo, Steel Tempest is that it is not always up. In order for him to get the whirlwind, he needs to hit two consecutive Steel Tempests and each has a base cooldown of 4 seconds. So if Yasuo does not have enemies to charge it on, there is a significant amount of time you can fight him without him having access to the whirlwind and consequently his ultimate as well. (Also on this note, Yasuo also needs enemies present for his mobility and to charge his E, a weakness you do not have as Hecarim) Additionally, you might have noticed that Hecarim can deliver a lot burst damage as well sustained damage. Because Yasuo is squishier, you can be able to win the majority of the battle in one good engage. Hecarim has good burst as well access to crowd-control abilities to negate their damage and Hecarim can hit powerspikes sooner than either those champions, you do have windows that you can use to take them out when the situation is to your advantage. Be sure to use them.