I'm not so sure FR using a GDS would have been such a good idea 10 or even 5 years ago.
The competitive environment has changed significantly over the last 10 years with plenty of smaller LCCs failing. FR has not always been such a giant behemoth and 10 years ago needed a strong focus on costs while its many rivals fell by the wayside. Had FR stayed with a GDS and become just another LCC 10 years ago, I doubt they would have been anywhere near as successful.
MOL may have pushed things too far with things like paying for the toilet or standing flights, but 10 years ago, FR made its name from going against the grain. As competitive environments change, strategy should also change - but a strategy that works now would not necessarily have worked 5 years ago.