I'll collect my notes and make a more thorough post about this later, but:

The history of bigger airplanes = bigger paychecks is one of linking pay to productivity. The more seats, cargo capacity, and range the more revenue is generated per leg (i.e. greater productivity per pilot). Using this formula the larger, long range aircraft produce a higher hourly rate.

In terms of pay year steps for various fleets and seats, there is a reward for seniority for sure!

UPS is just one operator that has successfully de-linked hourly rate from productivity. It can be done, although when you de-link pay from productivity you lose a tangible negotiating reference.