a super light roadbike will be faster, no doubt.
As long as the geometry and the fit for the rider is ok a folder will be only slightly slower. In other words if you sit on a folder the same as on a roadbike it will be only marginally slower ( due to weight )
Most restrictive is any position which is aerodynamically not optimized. I do sell a lot of extralong seatposts and shorter stems for just that reason.

But in general its a personal thing.

Jur what pixi dust you are talking about ? From Abu or BF fan ? That would be anybody who really likes his personal bike, right ? And there is nothing wrong with that.
I don't dislike anybodies opinion with a Downtube or Oregami or Brommy, nothing wrong for anybody to voice theirs.

thor