I don't care if the animation were terrible but the stories aren't even making sense anymore. Why not keep it simple like Might Dai vs The 7SOTM? Or Some backstory on things the manga never covered?
Had we gotten might dai vs 7 swordsmen, it would've destroyed the impact of might gai vs madara cause we would've known what to expect. So, Imo, it was pretty obvious why they didn't show this.
Fillers are a part of the animation experience. Bleach had them (some of the weirdest fillers ever!) The studio can put the breaks on the series and stretch it out. I have a feeling they are lining up their next big product after Naruto ends. Fillers are a way of controlling when the end actually comes.