I think the point Roos was hoping to make, in his call for professional umpires, was that their part time, semi-professional status serves only to hold back their development. I’m enlarging a bit on what he actually said, but he used the example of North Melbourne. He said they’d had another bad weekend, with another disappointing loss, but suggested that, come Monday morning, the players could return to their workplace, the training field, analyse the game, uncover whatever failings and deficiencies may have contributed to the poor result, than go out and spend time practicing the skills and tactics that had been shown to be wanting.
(Maybe using Norf as an an example of improvement through feedback was a poor choice.)
The umpires, on the their hand, who could also have made many, many mistakes in the same game, would be returning to their place of work - most likely an office - on Monday morning, and concentrating on their proper jobs, with no opportunity to analyse or consider their own failings or poor performance before the next weekend game, so they’re not going to be able to improve.
Having professional umpires may not be the complete answer, but it would help to improve, or at least arrest, a declining situation.
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* I do realise that everyone reading this posting already understands the argument in favour of full time umpires, but I had some spare time this morning and thought it could best be used by stating the bleedin’ obvious on DL. Apologies, one and all.