@livanbard
I actually really like the way this arc has progressed. I think there's less of a change of genre than it maybe seems like there is. Typical mainstream shonen mangas feature fight scenes and violence for the sake of flash and spectacle. Looking back at this arc, I don't really see the same emphasis on spectacle. The art style is one big reason; there is no squash and stretch, no fancy perspective changes or camera tilts. The backgrounds remain mundane even as the action increases. Posing never becomes too cartoonish. Character reactions are all subdued. All of these choices are really good, and keep the story's tone consistent with the world, so I don't get a sense of genre drift.
It's also worth noting that conflict and fights are inevitably necessary; the story can only say so much about Frieren in a vacuum before it becomes necessary to contextualize Frieren against the antagonistic others, and that necessitates conflict. Generally, I think the story has done a decent job of prioritising theme over aesthetics; the fights themselves aren't really the centerpiece, but instead the container for the story's morals.
Take this last chapter, for example. The thematic core of this chapter was about how an unbroken chain of experience and lifespan does not necessitate superiority; Fern wins explicitly because humans live fleeting lives in comparison to the demons and the elves, and so live much faster and brighter. This is an idea which is thematically very related to the overarching ideas of the story--namely, how Frieren's long life impacts her worldview. Fern's magic, and the entire fight between her and the demon is just the container for this idea. Whereas in a lot of traditional manga we see fights for the sake of fights and full-page single-panel spreads for the sake of aesthetics and they end up being kind of empty and meaningless, here the fight has been conceived for the sake of theme and character rather than spectacle.