I fully agree with you and to do so we would need reasonable options for both methods to find out if a consesus can be reached (by a poll for instance).
So far we have a reasonable proposal for 2 separate main tags
shop=hairdresser
shop=barber
For the method of using subtags there is
shop=hairdresser +
hairdresser=barber (for the barbers shop)
hairdresser= ?? (for the hairdressers shop)
Any proposal for a reasonable subtag for the hairdresser who is nothing but a hairdresser? Something which makes it clear to every mapper without reading some explanation in the wiki?