You say that but I don't think any arc has ever been as much filler as the Mage Exam arc. Granted I am only watching the anime and have not picked up the manga yet so my opinion is limited in that regard, but from an anime only experience thus far, the Mage Arc feels entirely like a waste of time.
We know Frieren is going to ace every test that happens because she's the most powerful living mage and its probably not even going to be difficult, which means that the arc is actually about Fern, but the story doesn't really follow Fern so what character development she is probably having we're not getting to see.
So what we're actually getting is a slow, plodding storyline of Frieren helping randos that we just met while characters we care about like Stark are sidelined, and I actually could not care less. I really liked everything leading up to the Mage Exams because it fleshed out the world, developed the characters etc. The Mage exams just feel like a very slow excuse for a tournament arc of sorts.