Agree with the beret problem - why can't they be taught the art of beret-wearing?
As for serving in the ranks, you then spend 6-9 months training someone to do a job for 15-18 months that they'll never do again, and lots of good potential officers would not join without a confirmed place on IOT, so you can't make everyone join in the ranks and only select for commissioning once they've done a couple of years.
Bring back five years as officer cadets, like my father had. Went to Dartmouth at 13, passed out into fleet training at 18, by which time he'd had a very good academic training, and learned an immense amount of naval knowledge, too. By the time he was 18 he could solder, weld, braze, rivet, and also strip and rebuild engines, weapons and basic radio kit. He was a seaman officer....