The curve is not there to fix eye focusing, it is to fix perspective problems.
I still use dual monitors myself, but they are always angled in towards me a bit, never flat and parallel. Once a display becomes big the edges of it start getting so far that perspective distortion might squash down the image to the point of small text being hard to read. If you curve the display around you then this does not happen. Be it as multiple display arranged around you, or one massive curved display.
The main benefit of a single large curved display is that you have the option of maximizing a window across all of it, doing that on a multi monitor setup is still possible but not quite so practical. Also works well for gaming.