This argument for various seniority systems could go around in circles and never reach a conclusion. Pilots rarely reach consensus, because everyone sees it from their own perspective - how they could be disadvantaged if it goes a certain way, or make rapid progress if it goes the other way.
By now the OP should have an idea of the pros and cons of typical seniority systems.
Next step in the process is for the OP to get his pilot union members all singing from the same sheet of music. This will be very difficult, but for the common good some will have to go the way of their peers. Until they do, and for as long as there is any sign of pilot group dissent, management will do whatever suits their purpose. Which is of course to drive down costs - at all costs. In today's anti-union world, the pilot group will have to put something useful on the table - like increased productivity - to have any hope of achieving change.