Why we rarely see magic circle during battle in Fairy Tail : Final Series?
I found this reddit post from 4 years ago that addresses this issue. Relevant comments from the thread:

u/AjStarGG: Well, the new studio is following the manga even closer than the old one and the circles are not in the manga.
u/GrumpySatan: The origin of the magic circles was to allow for them to reuse animation sequences. This saves a lot of time and money for anime studios since it helps extend the length of episodes without additional costs. Most animes based on popular and on-going series will use techniques like this. But it has become less popular as it generally degrades quality or breaks up the story.
It was actually fairly popular for fairy tail since they kept it consistent and it made some scenes (Mystogan v Laxus is my personal favorite) really good.

That might also be the reason why you feel the fights ended more quickly.