He is referring to the unprecedented level of transitions to take place between now and when the 73s and some of the 76s leave the property. It has been reported that there may be as many as 500 events. I believe that the TC will handle this just fine due to the following;

The number will he reduced by attrition as those that don't want to be international WB pilots seek alternatives. Attrition seems to have slowed, but there will still be some as attrition is ever present.

It is much simpler to transition an Atlas trained Boeing pilot with months or years of experience to a 74 or 77 then to train a new hire, shorter footprint, less remedials, less failures.

There are already about 130 in training, they have also trained numerous new CTIs and Check Airman

There is a ton of flying on the 74s with new aircraft arriving soon. The flying on remaining 76s could also increase. DEs are being deployed to bring the 74 aircraft on line soon.

Atlas has completed 6-800 training course each year for the last several years, albeit with delays.

Granted, some will experience delays waiting for classes and OE. It seems the company can afford these efforts as the profits continue to mount despite these challenges.