Ok Blacksheep, I'll resist the temptation raging inside me to wind up the class war plebs and tell you.
1. Career compression. It is very difficult even under the current system to get an officer through enough different jobs to prepare him for the the vagaries of senior officerership, before he is too old to command.My personal opinion is that we are too slow as it is. The human ability to think fast and make confident decisions without the occifying fear of failure clouding decisions is on the decline past our early twenties. This is to some degree offset by wisdom gained over the years, but it is no accident that in wartime the average age of senior commanders plummets. Nelson Captain of a ship at 21, Leonard Cheshire Gp Capt at 23 for example. We need people young/arrogant enough to have confidence in their decisions. To delay further the climb to command is a very bad idea.
2. Having suffered Initial Sea Training (IST) myself I feel we gained nothing from it whasoever. Practice bleeding combined with just a little bit of vicious treatment from a few chippy and bitter ratings who get to treat officers badly for once. I could already guess just what a crappy job pot wash in a high sea state was. I knew that the engine compartment would be hot and sweaty, and surprise surprise, it was. I knew that manning the gangplank in Brindisi would be boring, and it was. That quite simply is why I never joined to do those jobs. Don't bemoan your lot, change it.
3. On a slightly different note, there is a lot of talk here about ex ratings/rankers making better officers. I disagree. I think they are maybe more considerate/accesible to their subordinates and more popular as a result (though I can think of a few exceptions to the rule), but it is not a popularity contest. There have been "people persons" who have made "great" leaders, but there is more than one route to effective leadeship. Even Nelson sent his whole fleet to sea for three years while he took leave to shag his mistress. Hardly the act of a "people person". He was loved because he won. The winning is important, not the personality. So I don't believe that they make better or worse officers, just that they are generally accessible to their subordinates.