When you take a contract carrier, things will most likely be different in the event of IRROPS. It really comes down to how well the carrier is prepared to handle such an event, whatever that may be.

I don't think the issue pertains only to regional carriers because when IRROPS happen, it is usually similar to triage in how dispatch handles flights. In the same toll though, mainline and their contractors are different airlines with different dispatch operations by federal regulation. This likely causes disruption in the schedule because mainline Delta and contractor flights for Delta might not be on the same page.

The ultimate goal might be the same, but in reality it's two different companies trying to work together along with government services (ATC, airport services, etc) to try and fix an irregular problem. The end result isn't always perfect.

I think the main issue is with whatever carrier you fly. They ultimately have control over flights and whether you are delayed to the extent you are or not.