Phil Neville was one of the better right backs in the league. I wouldn't even consider comparing him to centre mids as he wasn't one. He was very much covering.
Comparing a winger going from right mid to right back is hardly an argument. Massively different set of skills between central midfield and right back.
Ronaldo is the best player in the world, hardly reflective of most players.
How many players play in two positions just as well. Most have a primary position, and any where else they play is secondary. I'd much rather get a right back in who excels in that position rather than someone who merely fills in when there's injuries.