Bottom line problem with B6 is that it does not have interline agreements with the other domestic carriers. This means that in IRROPS, all B6 can offer is its next available service or a refund. That will not help much in the case of massive IRROPS such as OP experienced, but that is not always the case.

This leaves one with the option of accepting the B6 reroute or taking a refund and booking whatever else is better.