Most of our new signings are squad players and need work to get up to standard - if they don't succeed they will be replaced by someone else. What they should bring is a hunger to crack the first team and willingness to work hard to get there. A revolving set of backup players who are desperate to succeed in SL may be the plan, with winners cracking first team at Leeds or somewhere else in SL, and the others going back to the Championship. So long as its just a part of the strategy its far better than keeping proven failures around for years.
MacDonald is a big unit and a real force in attack. But he played the vast majority of his NRL career on the wing as far as I remember - I really can't recall seeing him in the centres at all. No idea where he played at Norths but the chances are Leigh was his first extended period in the centres. No argument he'll need to step up a gear in SL, but hopefully he and Smith are aligned as to what he needs to work on.