I’ve seen it work both ways. It doesn’t happen often at all but we’ve had low seniority feeder drivers ( off the street hires) bump into packages. Usually due to being laid off all the time or doing a stint in the hub. They’ll bump in, dovetail in, stay 3-5-7 years. Sometimes less, sometimes more and then go back to feeders when it’s clear they will work every day.
I’m in a big hub, I’ve never seen a 20 wait to get into feeders. I have however seen many, many package car guys wait 20+ years to go to feeders only because they don’t want to be on call or work straight nights or get the left over “crappy” routes. Where I am at 20 years seniority will get you something decent. 25+ years and you’ll get something really good. So a lot of package cars wait till their seniority will do them some good. 5 years after qualifying for feeders they can get a tripled card. Even more great opportunities for them. Company seniority and dovetailing is a great perk in my opinion.