Let's look at Rousey's opponents (let's stick with UFC for now)
1. Liz Carmouche, age 35, still fighting, but not as a bantamweight ranked 3rd (4th) in flyweight.
2. Miesha Tate, age 32, retired in 2016. Probably the best Rousey beat. Only champion, though not at the time Rousey fought her. Last fight was against 6th (7th) ranked bantamweight fighter.
3. Sara McMann, age 38, currently ranked 11th (12) in bantamweight.
4. Alexis Davis, age 34, currently ranked 7th (8th) in flyweight.
5. Cat Zigano, age 37, currently ranked 8th (9th) in bantamweight.
6. Beth Correia, age 36, unranked, but just recently lost to 10th (11th) ranked bantamweight fighter.
7. Holly Holm, age 37, 3rd ranked (4th). Beat Rousey.
8. Amanda Nunes, age 31, champion, beat rousey.
Should be noted that Rousey is 32, but what do all these fighters have in common except Holm and Nunes? They aren't ranked very high in that bantam weight class. The only two that were both destroyed her in the ring. As soon as she started fighting legitimate fighters, she started losing. As the division continue to form, she decided to retire at 29 or 30. There's no more hiding, so what did she do? She quit... I'm not even sure how people are trying to argue counter to that.