Of course it does, when it can (must). But, it is not quite so simple.

Depending on the reason or flow control, carriers may be required to ration their arrivals/departures. That may be a straight limitation, but it may also affect departures in a given direction. It may also affect the capabilities of a given aircraft and distance (which roughly correlates to aircraft size, but only roughly).

PHL-JFK will be held (or cancelled) before PHL-LHR, if there are no other factors to consider. But, it is also possible that PHL-LHR can depart on a substantially different route and avoid coastal weather entirely. The JFK service, of course, cannot.

The ultimate goal is to hold aircraft at origin rather than in the air. That is why you have likely noticed a substantial decline in the old "holding pattern" problem.

But, bottom line, especially acute between RIC and BOS, is that the micro-hauls are held at departure (or cancelled) while long-hauls let fly.