For example the telephone system and the Internet are both fundamentally grounded on software developed using a waterfall methodology

Is this true? I can’t speak for telco, but I thought the internet in particular was developed incrementally with a lot of experimentation. I mean, yes, the experimentation resulted in RFPs and STDs. But I thought these generally came after the software was working. And as someone who has implemented a few RFPs, I would not say my approach was remotely waterfall.

Indeed my perhaps incorrect version of events is that the waterfall approach is represented by the big loser in telco, the ISO OSI.