Watch him again; he dithers at the base. Picks it up, looks, thinks, then passes. Against a faster defence, it's lethal, because it puts massive pressure on the 10 - and when Sexton is under pressure, he retreats deeper and deeper (in the first 30, Sexton was frequently flat, and static, and shovelled ball off; thankfully, POC, Fez and SOB were making silk purses out of sow's ears). Murray is inexperienced, but has a much crisper pass, and - crucially - breaks every so often, to good effect. He can also pass fast off either side; Reddan can't, having to spin around on more than one occasion to get the ball away.
Sexton's kicking is, simply, not up to it; he's back where he was when he was costing us games in the 2010 6N, kicking 40% if he's lucky. He would be much, much better off at 12, letting ROG make the decisions - which ROG does brilliantly - and giving himself a chance to play as a 5/8. Two playmakers is much harder to shut down, and much easier to bring the strike runners in. And, if we end up playing Wales, that's important, because the Welsh defensive system is all about line-speed.
Give Murray game time against Russia; and, against Italy, start a 9/10/12 of Murray/ROG/Sexton. With them bringing Earls (who had a very good game, btw) and Bowe in on the shoulder, we could start to make hay.