When I ride (western or dressage) I think of my stirrups somewhat like my reins; I can have a firm contact or a light contact and I should be able to change seamlessly from one to the other as needed. So, if I am walking, I only "feel" my stirrups. Someitmes , just for fun, I'll kind of "pet " them with the ball of my foot, reposition my foot and experiement with differen angles and feels. It's kind of a dialogue with the stirrup. Even while trotting along and posting, I should be able to make some minor repositioning of my stirrjup without losing it.
I do put weight down into my heel, but it doesn't stop at the stirrup; it goes THROUH the stirrup. The stirrup helps me to keep the front of my foot up and the rear (heel) more down but I think of the whole leg as going downward and backward with my heel linked to the horse's hind feet (mentally linked).
If one puts pressure into the stirrup so much and at such a forward angle that you counter the natural line that the stirrup leather or fender would take if it was freely hanging, then you are bracing. Other than jumping, I think that sort of bracing is not good. Even jumping maybe not good. JUmpers?