A. Break up the companies, assume mergers and acquisitions don't happen, consolidations never happens and that someone will be defiant of the law in the public interest at a crucial point
B. Change the law
It's important to note that AT&T was broken up and there once was many mobile carriers and there were many surveillance and spy programs going on during that time unabated and then they just bought each other up.
So instead of wishing on a hope and a dream that some invisible hands will orchestrate unexplainable market magic, let's just change the law. There's actual historical evidence of that working.
Or just prohibit them. That's a change to the law you can actually see is being enforced.
The problem with changing the spying law is that the spying is happening in secret, so there is no way to verify that they're not lying to you as they have in the past. Laws with no accountability mechanism are a farce. They need to be backstopped by verifiable structural inhibitions on the practice, like diverse decentralized infrastructure subject to competitive pressure and plausible independent reimplementation by anyone who doesn't trust the incumbents.
> someone will be defiant of the law in the public interest at a crucial point
This is required to turn back injustice. But it's more likely to be achieved the more people have the opportunity to do it.
The actual problem is the centralization, regardless of whether it's public or private. There shouldn't be two ISP options, there should be a thousand, so that anyone wanting to compromise all the traffic has to compromise a thousand independent entities, some of which can then be operated by stubborn curmudgeons who would rather loudly go to jail than silently betray the public.