I personally think it’s the other way round. Latu is a bigger body play’s deep in the line and has a bit more time or composure to his plays.Maybe the idea is for Sullivan to slot into 7, with Sezer at 6 to help guide him and bring Latu along slowly. If Latu shows he is more then ready, and Sullivan is guiding the team well, then Sezer becomes the back up.
I'm just guessing here.