I think the usage of the term "company seniority" is causing some confusion. There is no such thing.

Seniority is your position on the seniority list.

The pass travel, pay step, vacation accrual, etc. are all based on LONGEVITY, not seniority.

There are many cases where a pilot is ahead of another for a seat in the cabin but behind the same pilot for the jumpseat due to the ISL not being by DOH.