Interesting topic, OP. I'll show my appreciation by contributing the way I tend prioritise skills per position:
1 - boss the scrum, other than that don't be a liability on defense and clear rucks on attack nothing else is needed if you can boss the scrum.
2 - technically sound at the set piece. generally one expects more though but nothing necessarily specific- Bismarck's strength over the ball at the ruck, Dane Cole's running/support game, Schalk Brits' 7s distribution. Whatever you add, if its on top of sound technique at the set pieces then great.
3 - see loose head but only more so; more emphasis on the scrum.
4 - combination of support at the line-out and power in the scrum as well as clearing out rucks hard and monstering anyone getting close to you in the tackle
5 - taking responsibility for line-out calls and tackling like a demon
6 - tackle like a man posessed and play too the ball; compete for possession at the ruck
7 - one of the two main ball carriers, the main man do cause hurt in collisions be it in carrying or tackling; gain the hard yards bal in hand.
8 - a linking player, good all round skillsets, strong in contact but should be more rounded
9 - the general, the decision maker, the pace setter; should be quick to the breakdown and quick to make decisions and execute them accurately be it shifting teh ball, taking a kick or sniping off the base of the ruck. A crisp, accurate pass and good communication for directing the forwards.
10 - a 2nd 9 but being further out from the ruck/set piece will need to do the kicking if we are looking for yards. Generally take shots at goal but most importantly should be able to take advantage of good attacking ball provided by those inside him through an assumed varied skillset.
11 - if you have any sort of space you should basically be able to score a try whether through pure pace alone, elusiveness or power. One on one, you should be near unstoppable to contain.
12 - should be able to take on some of the responsibilities of your 10 and be complementory to your 13;
13 - defensively sound and organizing the backline defense. Dominant in the collision. Complementory to your 12; between you two you want someone who can make a hard yard or two and someone who can act as a playmaker in the midfield.
14 - See 11. But I'd want you to be able to act as a 2nd 15
15 - Kick returns whether through kicking back better or running well on a counter and knowing when either is best. Should be able to read play and join the line to create opportunities.
