Just catching up on all this and definitely agree with the prevailing sentiment.. feels like such a hollow award when some blatantly baffling decisions end up being the difference in who wins.
My theory is that umpires have so much going on, they often don't judge the game in it's entirety but instead it's moments that capture their attention. A particularly good couple of plays in the middle will resonate, and if they see a known superstar do some good things they are often going to have a unconscious bias. It can't be a coincidence that certain players always poll well, and others are often poll well under their performance.
Personally, I would love to see a small change that helps support the umpires rather than vilifying them - have an independent panel (say 3-5 commentators/journos/coaches) submit a shortlist to the umpires immediately after the came of who they felt were the best 6 or so players on the field. Then the umpires debate each on their merits, and award the votes. Still an umpire driven award, but instead of asking them to rate every player and umpire a fast flowing and complex game, make it somewhat easier for them.
If nothing else, this would have solved the JHF and Neale head scratchers, and could also see more forwards/defenders poll well as we could see games where more of the shortlist aren't midfielders.