Airlines receive thousands upon thousands of applications and to give feedback would be very costly and time consuming. They also like to have applicants that something that is natural not coached and giving feedback could ultimately do that. No airline I have heard of or come accross gives feedback.
Providing the airline with feedback on their recruitment process could improve a lot for the applicants and what they go through in waiting for the yes or no. I suggest giving them feedback and if you feel you have been hard done by or if there was anything they could improve on that would help you be more successful in the future then offer it to them. eg you may have felt uncomfortable with the size of the groups during the group sessions etc
Good luck!