That wouldn't happen. The discussion was about full timers changing classification. You are talking about a completely different thing. A PTer moving to FT starts at the bottom of the FT list.
If a 25 year PTer decides to go to feeders and become full time then he instantly goes to the bottom of the FT list. But if I would go from package car with my 15 years FT (23 years total) into feeders, I get dropped into the seniority line amongst all the other FT feeder driver, in my case 75/250ish. But some areas, apparently yours, will take a guy like me and put him at the bottom of the feeder list in 250/250 even though the guy in 249/250 may only have 3 months of FT seniority. To me, that's not right.
What's the point of building seniority if I can't use it to my advantage? The only people who think otherwise are people who don't have seniority and think they are getting screwed.