Yes, I agree, the Pro-Truth Pledge alone is not enough.
My most optimistic view of scaling the Pledge is that it would unite a large constituency of both private citizens and public figures who care more for the truth than advancing their personal ideologies, say 3–5%. Then, there would be both virtual and in-person communities of PTP supporters set up around the world who could advocate for the facts and fight misinformation in a wide variety of settings, while holding each other accountable.
In that case, it would have a pretty sizable impact on global society, in the same way that environmental activists have a sizable impact on society. After all, some of the tenets of the PTP ask signers to call out people in their social network who spread misinformation, and we know that at least some do so. This truth-oriented vanguard thus would apply positive social pressure to others.
While creating such a constituency is fundamentally important to addressing the problem, it would not solve the whole problem by any means. We would need additional mechanisms and interventions to address other aspects of the problem. Still, let’s hope the PTP can help accomplish the goals we set out!