If I am procedurally generating N buildings, is single actor for all the buildings more optimized or different actor for different buildings?

I am using CreateMeshSection_LinearColor method to generate large numbre of buildings, I have one actor per building, but the performance is low due to number of actors. As a way to optimize I thought if all the buildings were a single actor, with a single big mesh it would reduce the number of draw calls (as merge actor tool does something similar), but after just having single actor with all the building’s as single mesh saw that performance actually became worse instead of better. Why is this?

Try this:
Visibility and Occlusion Culling | Unreal Engine Documentation.

Thank you. But mainly the performance drops when I view the buildings from bird’s eye view as lots of actors need to render (also the buildings have no interiors and are simply cubes).