Yep it's the old flow through dilemma. For each SO upgraded is another that needs to be replaced. Direct hire FO completely solves this problem. If half the cockpit on a long haul are going to be SO now, they need more people in this rank and those people need to serve a very long time; the upgrade carrot will be their only motivation to wait it out.
Cadets with 0 hours have nowhere to go, as nobody (even Cathay) accepts the hours. 2x SO will make 7+ the norm, probably much longer even.
When SO was a transitional position of 2yrs and there was no Direct FO hiring, it made lots of sense. Now it's more of a career position in itself.
I guess if your goal is to be a career Cx pilot then it doesn't matter how long your an SO (minus the pay)