My niece will probably prefer the sparkly version of the princess. She's 10.
That's not regression, that's marketing.
Also: If Disney already has a dozen sparkly girly princesses, adding one with a different target market should expand their customer base. Adding another to the same group might just cannibalize sales of other existing sparkly princesses.
Because I spend a lot of time with her. Mostly at the hackerspace teaching her what a 3D printer is, how to make an arduino blink faster, and how to design files so that I can laser cut them.
But you said They presumably polled a test group and I meant, there's no evidence to support that.
I think the above costume was pretty tastefully "sparkled" up. If you want more, you could add the tiara from the movie or a more jeweled belt. Not even the Queen, mother of Merida and trying to shove the princess ideal down her throat, was _that_ dressed up for even the main event of the movie. I don't think this is any plainer or boring looking compared to some of the other Disney Princesses.
Also, not everything has to appeal to your niece or other girls or else we're telling them it's bad to be feminine. There's still a target audience for the Merida from the movie and it doesn't step on the toes of those that want a sparkly Princess.
> "look at this regressive stuff! How dare they!"
In this case it's regressive because Merida was originally a tomboy changed into the stereotype of a Disney Princess. I would not be outraged about this if Merida was originally that way in Brave.