Mainline calls the shots on which flights get cancelled when weather hits. And usually that means that the 19-76 seat flight gets cancelled instead of the 150 seat flight. The only time a feeder will cancel a flight is when there is no crews left for the day or a broken airplane that won't be fixed that day. Feeders will operate a flight many hours late because that's how they are paid, for completed flights, even if they are empty. I operated a flight from YYZ to IAH six hours late that was completely empty because every passenger was re-accommodated on other flights. But many times mainline will cancel a flight anyway.

Mainline also controls ramp, ground crew, gate agents, catering, lab service, etc. It is extremely rare that a flight is late because of a crew. Usually that only happens if someone accidentally sleeps in.