Tyson was a much, much bigger sports star than Rousey. She could be a great asset in a different, long-term way. But for a one-time publicity pop, he was a bigger deal.
The key thing here is, once more, it's not a one-time publicity thing. It's apparently Rousey signing a contract to be a full-time wrestler. That isn't a small thing.
The Tyson comparison would be more Mayweather vs. Big Show, imo.