I'd be interested in knowing what the difference between an 80 minute and a 40 minute hooker is. If it's purely fitness levels then our trainers should be able to address this.
These days I think the difference tends to be that a "running" dummy half will usually play less minutes. Most of the guys known as 80 minute players at the moment fall in to two categories: Leaders/micro-managers (E.g. Smith, Ennis, Farah, Hodgson, J.Friend) and pure tackling machines (e.g. McCullough, Lichaa, N.Friend, Srama).
Players who are moreso known for their running game tend to play less minutes, even though that doesn't preclude them from also being workhorse defenders or having other skills. I think that these guys are perfectly capable of playing the above roles, but their minutes are limited by the coach precisely to keep them fresh enough for their running game to be effective (E.g. Baptiste, Granville, Peats, Luke)
The final type would be a utility hooker (e.g. Kostjaysn, Cullen) who can play a little bit of hooker and a little bit somewhere else, so that your running hooker is getting a rest but you are not wasting a bench spot on a dedicated #9. We don't have this type of player on the books.
Finally, most of these "non-80-minute" hookers tend to play 55-65 minutes and just get a small rest. It's pretty rare to see teams play two guys each at #9 for 40 minutes like everyone did back in the early 2000's.
Regarding the guys we have on the books ... IMHO ...
Nu Brown would be considered a "running hooker"
Jayden Brailey would be a long term "leader/manager" type, but would probably be considered a "tackling machine" type for now, and it would be a risk giving him the job given his age and lack of FG experience
Cherrington would be considered a "running hooker"
So when people say we don't have an 80 minute hooker, I think what they are referring to is that 1) we don't have a leader/manager type player on our books to replace the Ennis role, and 2) among the available options, the best player (Nu Brown) is a guy who you would probably like to see given a rest ... since both his NSW Cup and (brief) NRL experience suggests he can be a dangerous runner.