All I'm suggesting is that if a particular user is concerned about their safety, I would suggest they take steps to insure it.
But if one wants to push for regulation to prevent the emergence of apps like TrueCaller, then perhaps we can start regulating robo-calls and sales calls more effectively? Then no one would need to install apps like TrueCaller in the first place.
And I'm suggesting that your proposed solution isn't reasonable, or even discoverable for the majority of people. Clearly this person was concerned about their safety. And clearly they took steps to insure it.
Arguing that the real problem is robo-calls is besides the point. It's like saying if people just drove safer we wouldn't have to have seatbelts. Or if I had bajillions of dollars we wouldn't have to have this discussion, because I'd be off on a beach somewhere. It's marginally related at best.
But if that's the line you really want to take, TrueCaller could have a "That was spam" button, and if enough people click it then it could block the calls. The faux caller ID part doesn't need to be part of the service.
Google Voice offers a somewhat similar service, but it flips the onus around. When enabled the caller has to identify themselves before the call can get through, and then the recipient can screen based on that. This approach is wildly more discoverable for the caller (who the information is attached to), and similarly filters out robo-calls.
But if one wants to push for regulation to prevent the emergence of apps like TrueCaller, then perhaps we can start regulating robo-calls and sales calls more effectively? Then no one would need to install apps like TrueCaller in the first place.