I was at a security presentation, oh, about five, maybe seven years back, by a company trying to sell, basically, SS7 firewalls, and advocating for basic security ideas that the Internet went through thirty years ago. "Hey, maybe do the equivalent of filtering your routes so people can't use phone numbers not actually registered to your network" and things like that.
The response you point out was exactly the ones that all of the big boys had; 'we don't need security, we just need to get back to closing SS7 to everybody that isn't one of the big boys.'
And the point the presenters were trying to make was 'that ship has sailed, you can get access to the network and start spamming SMS about as easily as you can get a gym membership these days, so stop living in the past.'