Interesting, having both the 800D and the S5 Mk2, I prefer the latter for stage-width, voices and bass accuracy (again, in my room). So actually my impression is the reverse.
The 800D has more bass impact and indeed more tweeter energy. It is more "fun", but less accurate.
At the high end my impression is, that even flatter on-axis response is not the important factor anymore. It's flat enough, especially in a stereo configuration, where the ear/brain listens for other elements like involvement and impacts, which depend a lot on the room and the spatial/temporal patterns of the speakers.