Can this concept of species be applicable for Paphs too?If it looks different, the name should different.
Your way is best. Making 5 distinct species.
Here is my opinion why...
Because they are distinct not only in appearance but also in locations. Keeping the "species" well separated with their own "simple" names eliminates confusion. Taxonomists who basically deal with only preserved specimens have no problem grouping under one specie name. But when you get into the horticultural growing side it makes more sense to have distinct names so as not to confuse the species with varieties.
I think varietal names should be reserved for individual variations that exist repeatedly within a specie population but not as separate populations on their own.
The problem is that you need to read Braem & Ohlund and Braem, Ohlund & Quené from 2004 ... In there it is made clear that "Cypripedium humboldtii" was never described. Dressler & Populin should learn German before they comment on German publications.The plot thickens!
A Nomenclatural Note on Cypripedium humboldtii (Orchidaceae: Cypripedioideae)
Pupulin & Dressler