As you said, it's a spin-off, and those are allowed to have a differing artstyle from the original source. Not every game in the franchise has to have a consistent style to it and some do take deviations to better explore the area that they want to expand on. There's nothing wrong with taking a different approach, especially since the point is to not focus on the core series, but expand a separate part of its mythos.
Also, I can't and never will see backlash where people are dislike spamming videos about the content (even if it's just things like GameXplain just showing it off) and a petition calling for its complete cancellation as well justified.