As far as Final Fantasy collaborations go this isn't nearly the most bizarre or inconsistent from canon.
We have product placements for Dre's headphones, Audi, American Express, Japan Airlines, and Nissin Cup Noodles in FF15. We also had that Yokai Watch x FF14 collab as well. And FFBE is all over the place from weird Christmas and Halloween characters to Dragon Quest to Monster Hunter.
At the very least Ariana Grande's sprite isn't too far off from the other FFBE characters. She at least looks more part of the FF universe than White Knight Noel (which is a surprisingly decent unit btw).
Personally, If it can get people that usually don't play Final Fantasy into the game (and into Final Fantasy) I think its a huge win. The young female demographic is something that FF severely lacks. She's got 43 million followers in that Twitter account linked in this thread, that's a huge audience to introduce the FF brand to.
FF needs to widen its audience to stay relevant and fund these over-extravagant over-budget games. The future of FF can't just be old JRPG fan dudes like me.