I think it is about time that EASA made it a requirement for AOC flying that all crew have permanent contracts, with their rosta declared in the contract.
I know from my own brief and unpleasant experience when I was forced by my employer to go freelance that it is detrimental to safety. The financial insecurity added to my personal stress before I even got to the aircraft. I had absolutely no rosta and was on call 24/7 which basically ruled out any social life. Then, as I had to take another non-flying job to make ends meet, I found myself reporting for duty on occasions not properly rested (maybe 2 hours sleep on one occasion). It was also very divisive amongst crews because some remained on fixed contracts, and others not.
If EASA made freelance flying illegal on AOCs it would put most of the cowboy operators out of business too.