I want to point out that lightning entering the Ethernet system without actually coming through the cable provider’s wiring is an edge case, but exactly the sort of problem I’m worried about.
That is, my guess is that 90% of home network surges happen from the copper that goes from outside to inside of the home, and the remaining are from induced (EM pulse) currents from INSIDE the home Ethernet wiring.
The longer a run of Ethernet the better it may pick up a lightning surge. From what I’ve read this danger starts around 30’ long runs.
Once the wiring is involved the next question is how will it find a path to ground? That path is often through a power supply somewhere. Once that gap is broken through everything in the way will fry as the surge arcs over. In these cases shorting (MOV) based surge protectors become co-conspirators by offering a low-volrage gap to ground.
Network isolators work by increasing the necessary arc-over voltage by 4kV at a time. This forces the surge current to look for a path with less resistance to ground which hopefully involves fewer devices.
And this is the thinking I've read lately. You may not stop the surge current, but you can reduce the total number of connected devices involved. If you fry a cheap switch instead of your switch, TV, streamer, PC, etc. it's a good thing.