Don't quite understand the logic here. The plane has non-working IFE for 4 consecutive flights and it is UA's job to pull the plane out of services.

On the ground staff, yes Air China staff handles the gate, but UA has supervisors on duty all the time. They do all the pre-checks and determine what special annoucements to make. I would say on average, Air China ground staff are fairly good, and desire a lot of credit than simply getting blame for something you are not responsible of. I guess it is easy to be critical than try to understand the process.