A few points...
Ben Hunt vs Andrew McCullough - Ben Hunt is the better player, McCullough is still the better dummy half. They're both guilty of being on auto-pilot at times, but McCullough has an underrated cut-out pass where he can put Milford over the advantage line which has been sorely missed and he just has better awareness overall around the ruck. There have been times where Hunt could have run but has just chosen to go with a nothing one off the ruck run. Defensively, there's no comparison, McCullough is head and shoulders above Hunt and unless Hunt really works on his technique it will always remain that way. As far as the team looking better with Hunt there, I can't agree with that at all. Across the past three seasons, the Broncos have played their best football with McCullough in the 9. If there was a common denominator this season, it's Kodi Nikorima in the starting team. Where Hunt does shine is individual brilliance and when he plays more like a half which is what we saw against Sydney.
McCullough is irreplaceable - This has certainly doesn't hold up anymore. Yes, the Broncos miss certain qualities he brings but it isn't like the Storm without Smith or the Cowboys without Granville the Broncos can still get by without him.
McCullough has signed on for four years - How many Broncos players were off contract this season? There were so many moving pieces that if you could lock down a few players pretty simply you'd take it. McCullough isn't a superstar, but he's a great club man and for Bennett very easy to get along with. Bennett could have taken the chance, punted him and looked to enter the market into the unknown but at a time where he was looking to sign Anthony Milford, James Roberts, Darius Boyd, Jack Bird etc. he was willing to compromise.