I wouldnt want to be putting the pressure of being the #1 striker on a 19year old kid from the academy, he may well be good but he hasnt got the experience of Zawada. He'll need time to learn his craft.
Not arguing with you, mostly because I haven't seen Supyk play at all, but Surman is only about that age, and I think the pressure on and responsibility of being a centre back is even higher than that of a striker. So, if he's up to it, then, just like Waineo, give him increasing minutes so he can have a shot.
I think that is mainly where I'm sitting too, I've not seen a lot of Supyk at all so not sure of what he is capable of. I think there is some difference between a defender coming on young as generally he is part of a back four and surrounded by older/experienced players doing the same job. Compare that to a sole front man trying to fill the role of the leading goal scorer, different kinds of pressure and less support directly around you.
Supyk may well be amazing, time will tell. If he keeps doing well in training then he'll get his chance, hopefully he takes it.