It's a 30 man squad with a salary cap, you can't have 3-4 back ups for each singular position its not plausible. Most those guys (except Hoeter who has only played 2 games in 3 years) are first man up for their squads in the outside back positions. I couldn't think of a bigger waste of a top 30 spot than Corey Allan...
Worst case scenario where both To'a and May went down, you have Makasini to go straight in and Laulilii (at either centre, or to wing with Turuva moving to centre). We are way better off playing and developing the young guys for a few games than Corey Allan. Corey Allan does nothing for the development of the squad and the young guys. Could you imagine the uproar on this forum if a young gun left because they were stuck behind Corey bloody Allan.
Beyond that, and somehow 3 go down, you have guys like Mapalangi and Tui'tupou who are capable enough and have First grade experience to cover a couple games. A guy like Allan does nothing at all. Mapalangi and Tui'tupou offer just as much, while on lower salaries and complimenting the development of the young guys.