Re: Asuka having a MMA background and style a main reason she was undefeated for so long?
Kind of. The MMA-esque style lends itself to being a more legitimate and credible style which makes it easier for them to be presented as dominant.
But the biggest reason Asuka was champion for so long was because the division was cleared out after she won. Her title defences after winning the title were Nia Jax, Bayley, Mickie James, Iconics, Cross, Ruby Riott and Ember.
The first thing out of the way. Bayley should've never been winning back the title anyway. Nia Jax obviously shouldn't have won either. And Mickie was literally brought back for a match because the division had no one else at the time and since she wasn't sticking around in NXT, she obviously shouldn't win either. It is my belief that they never planned for Asuka's title reign to be that long initially, but they were forced to keep it on her because of the lack of challengers.
By the time new blood came around, aka Iconics, Cross, Moon and Riott, it was at least 9 months into Asuka's title reign and they finally decided to do an invincible storyline champion with her, which is why she retained for the rest of her reign. The odds were constantly being stacked against her and she seemed to always weasel a win out of her matches. She was put against 3 other women in Iconics and Cross and despite the Iconics's perfect gameplan, she managed to get one of them out of the ring long enough to hit her finisher on the other and win. In the triple threat against Cross and Riot, she only won after hitting Riot with a shining wizard out of no where. Even when she was put in a street match against Cross, a match that should've been more to Cross's element, she still managed to outlast her and win.
The story was that Asuka was unbeatable, and that she always finds a way to win no matter the odds. The only person that she was afraid of at the time was Ember, who was the only person she had to cheat to beat. The story should've concluded with Ember beating Asuka in their rematch, to complete the story, but main roster wanted Asuka to keep her undefeated streak which is why she never lost