There is an economic concept called "ceteris paribus". In plain english it means "all other things being equal".

Using this theory, we can do two things. We can take each list of pilots at each separate airline, how many jobs in each seat, and time progress known variables (like retirements), leaving out unknown variables, and maintain the status quo in all other respects. We can calculate exactly where pilots would sit each year as other pilots retire. We can project what seats they'd sit in, etc. Each pilots can be given a "value" for their career. Not just where they sit in the end, but the entire value for the whole career.

We can do the same thing with both lists combined, moving pilots on each list up and down until the same values on each side are attained (or at least the same ratios to previous values are attained).

So a perfect example is the CAL list that was proposed. Many pilots have actually done a "me too" type analysis where they looked at where they were supposed to retire, and where they would end up on the combined list. If a pilot was supposed to retire #500, and now its #4,000 obviously that doesn't make sense. Same on the CAL side.

Some pilots are on furlough. They'd get zero credit for years they aren't flying, but then as pilots retire (ceteris paribus) they come back to work. They continue to upgrade and get a value for their career.

The question is simple, does a pilot on furlough at UAL have a better career expectation that one working at CAL? The entire career, including time on furlough.

Since UAL has mroe widebody jobs than CAL, and more Captain jobs as well, the argument is that a UAL pilot over the same number of years will have more chances to upgrade into higher paying equipment.

It doesn't take a genius to see that UAL's 3 times + as many widebody aircraft, with only 20% more pilots means overall we will fly bigger equipment over more time, paying more, etc.

I'd even say its "intuitively obvious even to the most casual observer".