What advantage does Signal protocol have over basic public key encryption?

Black-box solutions Vs P2P people power is a boring old conundrum. https://cryptome.org/jdb/ap.htm By "classical" thinking, "Assassination Politics" would have to be the best, tightest-security, more protected organization that has ever existed on the face of this planet. Just about EVERY powerful person would want to kill anybody who had anything to do with such a system. The codes would have to be unbreakable, the remailers would have to be certain, but most importantly, each and every participant would have to be perfectly anonymous to even have a prayer of pulling it off. Especially the operators of such a system. Especially them