What you're comparing is say the era of Ken Shamrock/Dan Severn/Royce Gracie versus the era of Jon Jones/Daniel Cormier/McGregor - the athletes have gotten way better, they mix the different disciplines instinctively and they're just much better fighters.
Same thing has happened in the womans game, once it became a UFC thing and Ronda paved the way for female fighters to actually get decent pay cheques, teams like American Top Team and Winklejohn started taking females in, and training them, getting them to spar with males and ultimately improving the skills bigtime in the game.
Ronda stayed static, and probably regressed because she started thinking she was the best striker in the world; in fights against one dimensional people like Bethe Correira, Alexis Davis, etc... she also got lucky in certain matchups - i.e Cat Zingano trying that stupid flying knee and getting caught in a clinch.
Miesha Tate was the first person to show that the mix of skills would trouble Rousey, problem is for how technical Miesha was, she was a 115-125lb fighter trying to fight at 135lb and just didn't have the snap to her punches.
Now people like Nunes are meshing boxing, BJJ, clinch control and wrestling together and Ronda is left with amazing judoka skills, a few holds (mostly the armbar and kneebar) and while she's got decent power, her striking is sloppy and she leaves herself way open, she's been stale while the game progressed.
She could still be useful in the division, but the prototype for beating her has been shown already... you won't see anyone rush her and rush into her clinch ever again.