There was an idea floated for DL/NW that never took off that seemed fair to me. Merge the lists based on ratios but keep the numbers separated by pre-merger airline.

When a UA pilot retires the UA pilots move up among the UA numbers and the same for CO retirees. If you are the bottom/top of the list today you are on the bottom/top of the list after the SLI. If you were going to retire in the top 1% you will still retire in the top 1%. It avoids the windfall today of an unbalanced integration and the windfall tomorrow of getting slotted behind a much younger group and stuck in a log jam.

No windfall and career expectations are similar.