Actually there's a pretty good argument that he is better on the wing. He's not great defensively so reducing his role there has been a positive (look at his possession metrics when him and MSL were a line and they were abysmal with frequent +/- in the negative despite high point totals). He's gotten better, but he's clearly below Tampa's two other top centers in that regard, and has often played wing even when there was injury to one or the other (see - when top C got injured in the playoffs, third C became second C instead of Stamkos moving to C).
Clapper's situation is notably different because playing D and playing RW are two wildly different positions, with different responsibilities and different expectations on play styles. If Clapper is getting drafted as a winger, he's going in the 150-200 range. But because he was *so good* at D, he goes much higher. The reason no one puts him on the wing is because #1D is way more important than #2RW.
I mean, you can disagree all you want but the fact is, Stamkos is a winger now, and there's sufficient proof of concept to put him there and expect his production to maintain. He has a top 10 point finish from the wing (with one still potentially pending) despite being post-peak and after injury, and has done it for long enough that it isn't a flash in the pan. I can't tell you how to value him, but if he's put as a RW he gets full value from me.