Rousey started out in the 145 weight class, she dropped to 135. In Judo she competed in the 154 lbs weight class.
As for cans, yes Cyborg has fought many because the talent pool is so shallow. The difference between them being that Cyborg has gone out of her way to find the hardest fights, as opposed to Ronda who went out of her way to duck Cyborg. Rousey has beaten Tate, and Tate has been among the best of the current talent. But that's it. Zingano and Correia are both tough and scrappy, but hardly gifted fighters.
And before you trot out Bethe's record, don't bother. I've actually watched her fight and I know who she's fought. She's a perfect example of the UFC propping up someone and feeding her to Rousey. If you didn't watch her fight, or know who she fought, you'd actually think she was a threat to Rousey - but her record was manufactured by feeding her people like Jessamyn Duke (who should never be allowed in the cage) and Shayna Baszler (which would have been pretty impressive in say, 2004). And she was fed those two specifically to build her 'rivalry' with Rousey by beating other members of the idiotic and generally unskilled '4 horsewomen.'
The UFC has fooled a lot of people into thinking Ronda was something she wasn't, which was a great fighter. They went out of their way to protect her from Cyborg, and Ronda didn't seem to mind a bit. Rousey even refused to fight Cyborg at 140, but then said she'd go back up in weight and fight Gina Carano. That's what made her a fraud, her bloated and fabricated record and her ducking of Cyborg. She was complicit in some of it, some of it was purely the UFC, but the result is the same. She mauled soccer moms and got her *** beat by skilled or powerful strikers.
Now the wheels will come off and she'll probably look back and realize what a fraud she's been. I don't think she even realized the extent of it because she was being fed a bunch of bull**** by that vulture Edmond. She believed she was the fighter the UFC said she was, some generational talent, and she thought she was an elite striker. Now she knows better, and I'm sure that's going to be a tough pill to swallow. At least this time she had an inkling going in, because she had been knocked out by Holmes. And notice the other difference between her and Cyborg (or any other real fighter), when Ronda lost to Holmes her former Judo coach came out immediately and said Ronda wouldn't fight her again because she doesn't handle adversity well. Low and behold Ronda didn't start training for her comeback until after Holmes lost - and don't feed me that crap about the jaw. Ronda didn't start training because she couldn't face Holmes, she didn't have the mental toughness for it. She's a bully, she's not a fighter.
A lot of people don't like Connor McGregor, but look at the difference between him and Ronda. They both lost and Connor couldn't wait for another chance at Nate, he wanted it immediately. It's the same with Aldo against McGregor - he wanted to fight him again the next day. That's because they are fighters, not bullies. Ronda lost and she ran away and went into hiding, she didn't want another shot at Holmes, she just disappeared and hid until the big bad wolf was gone. Unfortunately for her she ran into a grizzly when she came out of hiding.