Don't take that too seriously. I guess it just boils down to personal preference. It seemed to me like the changed the edges from the 6 and the X to the F and as a result it didn't edge quite right. I also didn't like the way they changed the volume distribution (didn't they add a lot of cockpit volume to the F that wasn't in the others?). Both of these probably contribute to it's being more difficult to roll. I bought mine more as a playboat that I could throw around but still do anything in versus buying it as a river-runner that I could do a little bit of playing in. Part of the reason I liked the 6 better than the F. I guess when I said it sucked, that was not about the boat in general but more how I felt about it in comparison to the S6. For what I wanted the S6 was much better. I don't doubt it will be a great boat for you.
As far as rolling goes, that's a tough one to help with without seeing you do it. But I've seen people with problems similar to what you are describing. Some people sweep roll up WAAAY forward (so far forward they're staring pretty closely at the bow of their boat). Often times when people who roll like that then hop in an edgy boat with a lot of cockpit volume, they struggle rolling because as they come up they reach a point where they're almost up and they stall out. Being so far forward with their heads, they are caught off-balance and can't complete the movement of shifting their weight over the boat without falling back over. The way I've remedied this in other people is to have them start rolling up in a more neutral position with their bodies closer to perpendicular with the boat. Once they're getting up, they can get a feel for the balance and power needed to roll the edgier boat and can start to roll further forward again once they get a feel for it.
I don't know if any of this makes any sense or is even close, but hopefully you find something that helps.
"The world would be a better place if everyone kayaked."-Brad Ludden (Valhalla)
"You only get one chance to run a drop blind."-DD