The no aeros FI restriction has always been a big anomaly - I don't know whether there has ever been an incident / investigation where an FI has been teaching aeros who hasn't had the restriction removed?
Ah well, we can all think of safety regulations that seem borne out of imagination rather than reality. I'd start with yellow jackets.
I think that any aviator, and any instructor, should try to continuously seek mentoring and push themselves towards best practice. We all know people who do this superbly (I used to fly a lot with the chap who is now CAA's Chief Test Pilot - he would insist on a full lessons-learned debrief from every flight, no matter how trivial, and I'll bet he still does), and we all know people who - well - don't: who regard their last skill test as a temporary abberation and they can slip back into more relaxed habits now.
I don't think that any branch of pilot has a monopoly on either mode of behaviour - but I can see why a PPL-only CRI should be a matter for concern. Hopefully the courses, skills tests and the periodic revalidations, will work to counter that, in the same way that line checks and company standards should for full time professional aviators.
G