I definitely see your argument, and as someone that has no desire to fly bigger, longer-haul equipment, it would certainly personally benefit me to have a pure longevity scale rather than an equipment scale, but I can't get past the revenue angle.
The guy flying the 1900 certainly has the same job and the same responsibility, but his company can't possibly afford to pay him $250/hr, because they just don't bring in the revenue with a fleet of 1900s in order to pay him that amount. The mainline carrier with the fleet of Boeings, on the other hand, is a very different situation. The 767 Captain brings in much more revenue for his company, so the ability to pay him that kind of rate is there. We have to think realistically about the company's revenue generation.