Nothing wrong with Barred Rocks, provided you get good, heritage or SOP type birds from good breeders. I picked up a cockerel that's under a year old and weighed over 8lbs, and the breeder had his cockerel pen on restricted feed. His laying hens typically weigh 8lbs by the time they're laying. As with anything else, the hatchery birds are going to be much smaller and less consistent.
I really don't think you can call one breed tough due to rigor. That has everything to do both with how old they were when you butchered and how you butchered them. Were they all stressed out just before you killed them? Did the killing go smoothly? Lots of variables on why the rigor didn't pass well, but I wouldn't assume it's because they were Brahmas.