Yes it is a one touch position. While lots of people dislike Osman it is a position that suits him massively, as he often has a "picture" before the ball arrives at his feet. I think Martinez has tried to shift Barkley into that role this season and in all honesty it has knackered his confidence.
He needs to get back to what he is good at, which is running at players from deep, shooting and assisting on the counter attack. I don't think Barkley is a particularly intelligent footballer and does not adapt well to other roles, I'm not sure that's something that can be coached and he'd be better sticking to what he's good at.
As for the back 3, well maybe. I suppose it is about getting the right players to fill the positions. Liverpools back 3 with Skirtl and Sakho are not comfortable on the ball enough. Right wing back is also a problem for them. I think they also lack a player like a Barkley/Gibson who can make it tick in midfield.