The whole in-class seniority is generally not a big deal. Usually the whole class gets the same initial assignment.

There are quite a few instances where in class seniority is a really big deal, but they are niches and rare. Such as, CA awards are not made in initial assignments since 9E has no street-CA program, but 2 guys in the same class could possibly be competing for a CA slot even while in FO training.

But, for 99 out of 100 new hires, in-class seniority is not really important and certainly not worth worrying about. The company can award seniority however they please since it's not covered in the CBA.