I'm not necessarily disagreeing but he's about the same height as Coloccini, who you love, and naturally bigger than him too.
Coloccini wins a surprising amount of aerial battles considering his size and he's a decent footballer as well. If Dummett is better in all these departments would you suggest that he could do a better job at centre back than Colo?
No, because Dummett isn't a CB. Certainly not yet.