No, actually I meant it's the other way round.
But after a direct comparison it seems like I was wrong...
See image below: the first crop is of a 3K render (a normal view, no spherical camera), and the second crop is of the 8K spherical
render of the same area of the scene.
It seems that the resolution of the area is just not high enough. To create a pano in the same resolution like in the first crop, it has to be at least 16K, if not 24 K.