It's a little bit of both.
Cyborg is actually legit good. Ronda was a noob in a time when other people were also noobs. If you watched her fight with Camouche, she went that head lock on the ground and let Carmouche take her back and ended up in a face choke. That shows that she was still transitioning into MMA or even BJJ grappling. That's one of the moves they teach in MMA or BJJ self defense very early on. I am not saying Ronda wasn't good or she didn't have that knowledge, but she was still transitioning and learning the "MMA game", she just was way ahead of others in terms of learning curve.
Cyborg has been immersed in MMA and I don't see any of these women beating her anytime soon.