I don't know if it has changed in the last 2 years since my youngest went to OASC - he didn't pass but the Sqn Ldr in charge told me that even though the pass mark was 120 (IIRC) they weren't actually selecting below 145.
Now I have no idea how relevant the tests are to what an RAF pilot is expected to do nowadays but if you have a pass mark and people achieve it, why filter further?
You are denying suitably gifted people the chance and creating an elitist system - no wonder people don't want to join.
By setting the bar very high and then failing to put them through the training system in a reasonable time frame - you have two elements that might just show why recruitment is an issue.