Seniority is at least an objective measure, even if it is a terrible one. Besides which, no one says that's how a union has to work.
Hey, I need a new webcam for interviews because this 720p can’t seem to get decent lighting really does a number ob me there.
/s
The union can post jobs internally and they have to evaluate internal candidates first. Some places I’ve worked even have it set up so that internal union members are sent to school for training before they will open it up to external hiring.
Credentialing. Union can enforce specific credentials that would then keep people otherwise qualified out.
I think these (which are scenarios I’ve seen) are worse than the current system where if you have the skills and can demonstrate them, then you can get a high paying job.