It was well played by Wilson and well worked by Newcastle down our left. But Romero, who looks behind him before the ball is crossed, so he knows that he's there, should challenge for that though he was on his heels (but glad you've rewatched it and now can clearly see it's not on Dier as you claimed). There is NOTHING wrong with Dier positioning for the first, there isn't anyone to mark, he's exactly where he should be (Skipp is the player out of position, left Reggie with a 2v1 or maybe could be argued that Son should have been out wide to help, while Skipp's role would have stayed narrow, I don't know what their specific instructions are here. Romero is positioned where he should be as is Emerson, all be it he is in a 2v1 situation against him at the back post, which is quite usual to see. ALL the back 4 are positioned well, including Reggie who's needed support from Skipp/Son).I've watched the first one a few times. Have to give credit to Wilson for the movement, it was very, very clever to hide behind Romero and then get around him in the time it took the cross to come in. Dier was still marking no one though. He was, as he often is, stranded in no mans land and not really adding to anything.
As for the 2nd, whether Romero missed it or not isn't important when Dier tried to head the ball, failed, fell over and kneed it into the goal like a complete pleb,
As for the 2nd - Of course it's important that Romero missed his header, it's no different to a 'Keeper claiming a cross and missing it and a goal results. It looks a mess, so always looks bad on whoever the ball comes off, but taking charge in the box is the responsibility of the player that demands/challenges for it, it changes that defensive dynamic in that moment. If that was Lloris claiming that cross and not making it then it would be his fault, not the player the ball comes off as he has little to no time to react.
But I'm not even on my high horse about Romero's poor performance in the first half (loads of missed timed tackles, got beat clean for their goal) because he brings a dynamic to our game that I think we need and have lacked for ages now (front foot and aggressive) he's young (especially for a CB) so will make mistakes every game (Just as he has done multiple times in every game he's played for us) but the balance of the team has improved.
But make no mistake that playing alongside him means whoever that is, is going to be left isolated when he misses his tackle/gets rolled/calls for a ball and doesn't make it and they are left mopping up after him, and that's been Dier. So next time we concede, just hold your horses before you point a finger, take the move back and see where it stems from (as per the Villa goal before the international break, as right now Romero for all the aggression he brings he's been the route cause or instrumental in the build-up to the oppo goal).
It will take time for a partnership to form but our best two CB's are the ones selected by Nuno yesterday.