All the RDC’s where on their own backbone?
"All of the RDCs were connected via backbone connections, so latency was negligible, and bandwidth was massive."
Just also happened to be sharing the corp firewall too.
If it’s important enough to segregate on its own links but needs firewalling then it’s an own goal to use the enterprise firewall for that shared task, a dedicated device with enough capacity to handle the throughput achievable in those “backbones” should have been implemented too.
I suspect those RDC’s had their own “backbones” but the testing stuff relied on those same “backbones” and didn’t have dedicated connectivity as the story hints at.