Question on optimisation of modularity and procedural generation of buildings

Hey folks, so I’d love to get some more insight into the optimisation of buildings in Unreal.

My question is if I generate a building in Houdini/Blender, would this generated building have a worse impact on rendering in Unreal than if I constructed it manually with modular pieces (excluding time as a factor). I know that prcoedural is a massive timesaver, but is there an impact on performance because I would be importing a single, huge asset?

I have seen how they constructed buildings for The Witcher 3, and it is entirely modular buildings, so that if only the upper half of the house is visible, for example, then that cuts how expensive they are, so there definitely appears to be a benefit to modular construction. Is this lost with the procedural generators?

Am I misundrstanding something about the procedural outputs from Houdini/Blender?
Are they worse for performance?
Can they be broken down into separate pieces when imported?