Precisely. Its not his ability to tackle. Its his ability to read attacking patterns that don't always come from the simple, clean breakdown, that you get in League. However, he's been playing Rugby for several years now, so it would require a particularly skilled attacking combination to be able to get through him.
Barnes is simply not in the same league as O'Connor is in attack, though defensively he has the wood on O'Connor, simply because he's far more of an 'offensive' defender. Cooper is the problem./ Sure he can be hidden in defence, but who comes into the line for him? Ioane?
Defensively, Ioane at 10, and Beiber at 12 could work, though I don't know how long Diggers' shoulders would last with that arrangement. However, it would also leave Quade out the back, ready for a rapid counter-attack as he wouldn't be buried at the bottom of a ruck.