The thing is that Ember hasn't been booked as strong as Asuka who has steamrolled everyone except Bayley, Nia and Mickie James and maybe Bayley could be debated, Ember is "undefeated" (except at live event matches where AFAIK she's lost to Asuka in every match) but her wins aren't as dominant and it makes everyone she beats at least look like they could some day be on her level and beat her opposed to Asuka who completely outclasses everyone who is still in NXT that she's faced.
I agree about the character issues but that's on the creative end and I hope they give her some actual time to develop that, the issues with the presentation issues could be explained fairly easily, in terms of match quality Ember/Asuka is the best choice. Save Nikki Cross for Ember after Asuka is gone, assuming of course Ember beats Asuka, which she should but we'll see.