Both of those things can be true, the smaller the bandwidth is you need the more extra information you can pack in your channel width to make it possible to reconstruct a lot of data errors. And modern digital codecs can squeeze data much further than plain analog audio, hence it's easier to get it to go long distances if the system were to have that as a design goal.

Yup, but I was also specifically pointing out that opus is quite tolerant of missing data (part of the article). With 90% data loss you can still pretty intelligibly understand what is being said.

So long as you can get pops of decodable signal, you'll be able to understand what's being said. Using a more robust modulation scheme would also go a long way in improving reach.

AM gets it's range benefits not from the modulation used, but from the frequencies it occupies.