Its not necessarily 81% for the full 5 years. 2 weeks after joining recently, we were told we could be full time for this winter, and the previous years intake have been offered full time positions. I doubt I'll be PPY at all to be honest, maybe one year at most. Granted it's always possible for those 5 years if the company decides to scale things back so it would be prudent to budget for the full 5 years being PPY but I can't see it myself.
Regarding the pay, yes it's a shame it's not full time from the start without the £7k OCC reduction, and for those who can't afford the pay cut for a year, it's a pity not being able to apply. If you can look beyond the initial figures though, it does get significantly better, 5 years in and full time command ready, the basic is about £70k. With the variable pay on top, day off payments, 10% pension, private health insurance, discounted holidays and so on, it all adds up to a decent package.