That's not true - only instructing for issue of licences and ratings.
People doing biennials, differences training (tailwheel,retracts, microlight...), currency checks or syndicate checkouts aren't required to work under an ATO.
At the same time, most instructors - even if they are largely freelancers - have a relationship with an ATO or equivalent that they can and often do function within for legal purposes.
So it's really not as bad as you fear.
G