Chatted with my grappling instructor friend on the Mayra and Dern fights, roughly paraphrased, Randa and Mara screwed up 5 moves ago when they tried to sit up out of a triangle/armbar setup instead of staying tight, keeping the opponent's hips down, and working to "swim through" the way Ribas did against Dern. Trying to sit up and posture out of that position doesn't work unless the other person's a newbie or it's later in the fight and you're both covered in sweat. First minute of the fight against legit grapplers? Yeah you saw what happens then.
He also noted that as good as Dern is, going to the ground with her is not an instant submission. If you stay composed, don't make stupid mistakes, and make her work for her positions instead of giving them away, you can keep her from doing too much until the clock runs out or she tries to force something and gives up an opening for an escape. Which makes sense since both Yoder and Ribas survived on the ground just fine against her. Unfortunately, composure in the women's game is rather lacking. On one hand it makes for a lot of fun scrambles and sequences, on the other hand, it gets you tapped out fast against grapplers who know what they're doing.