DFC: interesting how flying school environments can be so different. My CFI wouldn't know money if it hit him in the a**se and I don't know any CFIs who are also school owners and who might therefore prioritise income over safety.
A regulation requiring 5hrs (or whatever) on type before you can instruct is a hopelessly blunt instrument because your 5 hrs could be 5hrs solo with absolutely no instruction and no serious content other than bimbling round the sky with a couple of landings. However a regulation requiring a checkout on type by a supervising instructor with appropriate experience would give you most of the basic knowledge you would need to operate the aircraft safely (talking about types within the SEPL rating here).
Even 15hrs is a hopelessly unrealistic minimum in my view. In the UK clubs and schools would just ignore it or find some way of fiddling it because the costs of giving all new instructors 15hrs on the types they hadn't flown would be prohibitive.