Though it was always claimed that ex-UAS mates were more likely to 'go all the way' and to successfully pass through AFT/TWU, and though it was said that ex-UAS mates were more likely to serve to 38/16 (and beyond) I am not for one moment suggesting that the RAF should aim for an all-graduate pilot entry, though three years on a UAS is a remarkably effective and cheap 'filter'.
The existing system, and the existing mix of DE chaps (fresh from A-level) and grads, works well. Some blokes would be useless to the RAF at 18, but are a great bet after three years growing up and enjoying UAS etc, while others would be past it and stale if you waited a moment past their A-level.
Once people have done two tours they're pretty well indistinguishable. Some of the best and brightest are DE, some are ex-UAS. The existing system ensures that you get the best from both worlds.
If it ain't broke, then why fix it?
And if it needs fixing, then is dropping the entry standard the right way to do it? 20 years ago, only the top 2% went to Uni, and the RAF relied on this top 2% to provide just under half of its pilots. Now the top 40% go to Uni, and you're talking about recruiting only from the rest......
And with regard to your specific points:
"Shallower learning curve" - nonsense - it depends on the individual and a three year UAS course can provide a firm foundation that compensates, and a knowledge of what "you're letting yourself in for" that provides useful motivation.
"Not enough ability to take discipline" - unfounded over-generalised prejudice.
"Career compression" - would be a good point if DE blokes' younger age wasn't used to allow an inefficient system to give them longer in pointless andunproductive holding posts.
"Probably serious girlfriend therefore unwillingness to deploy" - or more eager to get away, perhaps!
"Useless knowledge about Geography, Law, Fashion, basket weaving etc" - it may have been different in my day, and/or at the UASs I know about, but about nine in ten guys on my squadron were studying Aero Eng, Mech Eng or Eng. I was the only arts undergrad in my year, though there was a dentist the year above me, and a biologist the year below.
"Greater expectation of wage etc therefore more disappointment" - maybe.
And I stand by 'maturity'. Most 18 year olds regard 12 years as a life sentence. Most graduates view 16 years as entirely reasonable. Nor are graduates the 'inflexible' 'set in their ways' chaps you caricature - most have trained minds that are more open than those of callow youths with GCSEs!