It is no different coming out of an Airline with years of training experience, you still need the GA ratings. Even more bizarre under the new rules before you can be promoted to be a training captain within the Airlines you have to have an instructor rating. I have witnessed several senior captains who have been out of GA for 30 years going off to the local to get a Grade 3 so they can become a training captain. It is one thing to master the dreaded Cessna 150 after a Boeing or an Airbus but that FOI Exam, or whatever they call it, is a little doozy. I have never read anything quite like it.
'Tis the rules chaps and flexibility or common sense is a strict liability.