I tend to agree with everything you say Daz and respect your opinions, but disagree about Nathan possibly moving to hooker. I concur with everything you described in his strengths and weaknesses. You must remember he is only 19 (might be a song in there). If you compare with say Brodie Croft/Ash Taylor there weaknesses would also be vision and creativity too. I put it down to age, experience and confidence.
The big question is will Nathan develop these attributes? He seems to be surrounded by great centres of influence and I hear nothing but how hard he works on his game, so you would be optimistic he could. Not comparing to Cronk, but he also had to work on developing these exact attributes and it appears Nathan is dedicated enough to also. Don't forget Cronk also started as a hooker, so the skill set is somewhat interchangeable.
You pay more for 7's than 9's, so unless we replaced him with someone in-house, would cost a premium to get another number 7.