I find this entire idea absolutely hilarious. That anyone thinks they would've been able to watch everything on TV they wanted for $15 a month or less when the cable industry was charging well over $100 a month prior. Anyone who believed this would be the case is... well, HN rules would rather I not be that blunt.
Netflix briefly enjoyed this width of content solely because it was viewed as an additional revenue stream and not the primary one. As soon as streaming became the default, it was necessary to actually bring in enough money to make multi-million dollar episodes, and that means not selling content to Netflix for pennies on the dollar. Netflix wisely used the interim to build it's own first party content library (which everyone else already had), while everyone else had to build the distribution network (which Netflix already had). While they did it in a different order, they ended up placed about even with other TV companies in the long run.
The cable industry admittedly also included sports and some other live content--some of which is on various streaming services. And some other content is only available a la carte. But I agree with your basic point.
A hypothetical all non-live available digital content for one monthly price would probably be over $200/month.
The good news for someone like myself is that I can get tons of content (and access to more a la carte) for under $50/month. I could add a live streaming service and I'd still be paying less than my cable TV bill used to be.
There are definitely some efficiencies... and inefficiencies of the new model. Used to get 200 channels for $100, and now I can get like 6-8 streaming services for that. But since it's a la carte I can pick which ones I use, including spinning down to only one or two.
The sports surcharge model I'm especially glad to get rid of. During the pandemic, the Chicago Cubs decided to launch Marquee Sports Network, and require every carrier in the Chicago area to subscribe all customers to it for roughly $7 a month... or not be able to carry it at all. The ridiculousness of it is like if you were forced to buy HBO by your Internet provider.
IMHO, the city of Chicago should've kicked the Cubs out of the city over it, but sports teams have too much power over municipalities.
(Note that the carriers are presumably contractually required to deny you are being forcibly subscribed, but every carrier's sports fees uniformly went up approximately $7 a month when Marquee launched.)
Steve Jobs was able to pull this off for music (iTunes). Netflix folks should have tried harder to become the default streaming platform.