I just asked my Zürinet provider if they are willing to bend their prices for me or else it's a Salt/Sunrise deal (that's what I call talking out of a position

).
So they called my all-in, and they stated that with them (Internet Group) I have the fiber to myself, whereas with Salt and Sunrise I need to share the physical medium with many more customers, making it "much slower in response times". And that it's a "completely different product".
Now I wonder what actually is different? 'Cause the only stretch of fiber I have to myself - I guess - in both situations is the one leading up to my flat from the basement. Anything that reaches the first 'core switch' of the building - or area I'm living in - will then be routed onto the backbone network of the provider. So how is this different in the two ways? I guess Sunrise is also using the Zürinet (in B2B I know they rent the fiber from Swisscom).
I consider this statement from the Internet Group proofless (=BS).
It would certainly be cheaper for Sunrise or Salt to have less fiber capacity and spread it more clients (more leaves than spine in SDN lingo), however, this would make them build a parallel, Zürinet-light, which I don't think they want or can do - so my assumption is that the physical medium is also the exact same.
Could anyone please confirm or deny the above?