I think we missed the work rate of Tim Brown in front of the back 4 this season. Although Dura and Siggy were below their best, at times everyone was streaming through our nonexistent midfield. Makes the job a lot harder! Boxall was on a hiding to nothing in the limited chances he got for the same reason and also back combinations take time to click so the odd game here and there isn't really a fair reflection of his ability.
I think Boxall looks good technically, reasonably strong, reasonably quick, and a good reader of the game. The only downside I can see is that I think central defenders work best as a complementary pairing (which is part of why Dura and Siggy worked so well in previous seasons) and Boxall strikes me as the same sort of CB as Dura, albeit less experienced and confident at this stage. Siggy would complement Boxall better than Dura would, but Siggy was clearly the weaker member of our central defensive pairing last season so you would think if we are dropping one of our starting centrebacks it would be him.
However, Ernie has said he wants to play with fullbacks effectively acting as wingers and 4 creative attacking players. If you want to play with your fullbacks bombing forward on attack then you need at least one defensively solid holding midfielder, possibly 2, who can cover and slow down counterattacks if you lose possession with your fullbacks far up the pitch. Therefore there might be potential for either Dura or Boxall to pop into a DM role to screen the defenders and cover the inevitable open space caused by having attacking fullbacks. I wouldn't want both Muscat and one of Boxall or Dura as a DM pairing because I would doubt their ability to distribute the ball to those attacking players. But I do think that Manny could be an effective attacking fullback - he's got a decent cross on him and has played the role a fair bit under Ricki anyway (although maybe not as attacking as Ernie is planning). So if Manny is at RB then I think Boxall or Dura at DM plus a ball-playing deep lying midfielder (Simon Ellliott from 4 years ago would be perfect) could be effective. The key being, of course, to find that deep lying distributing ball-playing midfielder...