Honestly, for a Yoasobi song, this does exactly what you expected: a catchy beat, interesting chants and lyrics that perfectly captures the themes of the show.
However, when you consider the nature of Sousou Frieren, which is an anime that does not follow the usual fast-paced and excitement of its fellow fantasies and is more of a tranquil and slow journey like Violet Evergarden, the OP really feels out of place here. A rare case for Yoasobi as the band usually has perfect ops or eds for the respective anime (most recently Oshi no Ko or The Witch from Mercury). Compare that to the ED by milet, which suits the show way better than the OP.
All in all, while Yuusha is still a solid song and definitely something which can be jammed to, it is just not the right for the atmosphere of vibes of Sousou Frieren.