I agree with you in principle, but I'm not sure it's possible to start Hook at 10 now. For me it will always be his "proper position", but he's never had a decent run of games there. Moreover, game management - Hook's widely-acknowledged weakness - will be crucial against Ireland. That's why I'm sympathetic to calls for Jones at 10, although that would be a ridiculously harsh call on the excellent Priestland.
I believe we have to find a place for Hook, and that place is probably 13 at present. Jon Davies is a good player but the wrong partner for Roberts IMO. Williams is a better option but we really need a creative midfielder to complement Jamie. Also, starting with Hook at 13 means he can cover 10 and 15, possibly freeing bench space for "luxury" impact forwards like Powell, Ryan Jones and/or Brad Davies. Against an Ireland side whose biggest edge over us will be up front, that could be very handy.