One thing to remember is that this doesn't necessarily mean 700+ unfilled positions to cover specific flying (i.e. 50 unfilled vacancies on fleet X means shortages/green slips for that fleet).

The company must offer positions to existing pilots (post as a vacancy on AE) before a single new-hire can be placed into that position.

By having all these unfilled vacancies, the company gets flexibility to place new hires where there are openings in the training pipeline, as well as to backfill existing-pilot-movement and right-size staffing.