The PL, especially Man City and Liverpool, are a world away from where we are. At this level we need players who are, first and foremost, strong in their own position. Everything else is a bonus.
It's no coincidence that we looked a much better side when we had Long and Ruffels at full back doing the simple things well. Eastwood was solid, Dickie and Nelson made less mistakes because they could focus on their jobs rather than trying to fill in for others. Kashi doing the dirty work, Brannagan able to influence more going forward. Sinclair/Mackie chasing down each ball, hassling defences. Creating pressure and space for Whyte, Browne, Sykes to play in.
At it's not like Long or Ruffels were ever one dimensional. Against Charlton, both were running at their defenders in the last few minutes, both have created problems in the opposition box at set pieces.
Of course, everyone is replaceable and no one is guaranteed a game. But I'm sure we will be prioritising other positions over full backs this summer.