For me, and what my supervisors and managers saw, was the willingness to learn more. Senior people are just that, if you can work outside the box, and can be changed around, and not stuck in your ways, its a plus... we have guys in their late 50's to 60's.. still doing PUD, why.. because its all they know, have they applied to be linehaul, sure they have, but them them-selves have admitted that they are stuck in their ways, and just rather, go to work, do the same thing, go home...
Just because some have been their longer, doesnt mean they have more "knowledge"... heck, the most senior supervisor in charge of PUD, has never actually done a PUD route, and so he relies on his lower downs, to inform him of the needs and wants...