The expo on elevator does not fix any problems. I'm assuming you have a perectly fine servo and the problem is that the linkeage on the Hornet is super sensitive, similar to a Tam F-16, where you don't need that sensitivity. Now if this thing is flopping up an down and the control surface deflections are clearly noticeable, then there is another problem somewhere.

Nothing wrong with using expo to overcome servo sensitivity, that is exactly what it is for. But now I think you have a another problem if you say you already have expo applied and it still jitters.