I think you're struggling with the concept of players having utility value. And if McInness has a running game good enough for him to convert to being a representative lock, your argument that he lacks a running game falls away badly. As for creativity around the ruck from dh, not the best, not the worst which is about the same as Robson frankly.
Players have played in multiple positions during their apprenticeships so we can't say they have never played certain positions definitively unless you've really followed and studied their junior days. If a half had to shuffle one out, it is doable particularly as they already defend next to centres and edge backrowers but, alright, if I have to pick one, Luai.
My bench is a hooker/small, mobile middle, a middle/edge (that can play centre really well if needed and let's face it, shit happens in games like, send-offs and such, so ...) and 2 pure impact middles given that we have enough edge backrowers that actually do play big minutes. No one should be playing 80 minutes at lock in Origin. At edge maybe but Origin is too quick and high intensity. Maguire needs to get his middle rotation right first and foremost to be any hope.