Isn’t wire also a shared medium? It’s not that there is an end-to-end circuit when you connect to another machine on the Net; your packets will be send along with others’.
That's a really tricky question. At some point, the packets are going to share a link with those from other customers, possibly oversubscribed...
Cable internet is clearly a shared medium at both the physical and link layers.
Fiber like GPON is shared physically-ish, but DWDM isolates individual waves so thoroughly that it's hard to think of that as a shared physical medium unless you're thinking about backhoe fade and the like.
With DSL, do you consider the DSLAM?
Etc
This is incorrect. GPON does not use DWDM, or any individual waves per subscriber. GPON is a shared medium with one wavelenght used in the upstream and one wavelenght used in the downstream direction. Each subscriber is allocated bandwidth on the shared medium.
Not even next generation PON uses DWDM. Next generation PON still uses on upstream and one downstream wavelenght per PON tree, but there can be multiple PON trees on the same backhaul fiber. It's more like a CWDM overlay of PON trees.
The only PON that uses DWDM is WDM-PON, but it isn't deployed commercially at scale yet.
not since you have had ethernet switches.