Nolan has played at the top level domestically for many years, several leagues higher than some of these referees have ever operated, and will have seen the standards of refereeing at Premier League level at close hand, so he's arguably better qualified to judge the performance of most of these lower level refs than either they (and in some cases perhaps even their assessors!) are.
I can see your point that shouting at incompetents is perhaps likely to make them react defensively and exaggerate that incompetency, but it must be very frustrating being told what you can and can't do by someone who hasn't operated close to the level you've achieved.
Earlier this season, Premier League ref Mike Jones came to referee our home game against Swansea in the FA Cup, and his command of the game was such a stunning improvement on what we're normally used to seeing that many fans went home talking about how good the ref was. And that doesn't happen often. I can barely remember Jones putting a foot wrong in 90 minutes, and unsurprisingly both managers were very calm throughout a very exciting game.