I would think that outright collusion would be hard to accomplish for people writing centuries apart, but I don't think it's remarkable at all for one writer in a religious tradition to write in accordance with past writers in the same tradition.
That comment just smacks of cynicism.
Also, scriptures go through selection and editing processes for consistency. It's not like God wrote the Official List of Official Prophets and handed it down from on high; over the centuries, people have made judgements about who is and isn't a "real prophet" or source of "real" scripture (e.g. "Moses, Daniel, and Matthew are in; Mohammed, Joseph Smith, and the Baha'u'lla are out"). Whatever the criteria used, as long as they're applied consistently, they'll result in a consistent message among all the sources that are included... even if the criteria are completely arbitrary and the authors have nothing to do with each other.
And the reason the above comment smacks of cynicism is because you are assuming that God did not call the prophets. Rather you are assuming that men are the ones who have designated who is and isn't a prophet. If that were the case, how does that explain the people murdering some of the prophets who came to them? Actually, as is indicated in the book of Jeremiah, God did ordain prophets even before the world was thereby creating an official list of prophets.
But there ISN'T "coherent and cohesive agreement". Religion and gods have been some of the most controversial, polarizing subjects that humanity has ever considered. Screening out only the opinions that agree with your particular beliefs creates a false impression of agreement.
You are conflating all religions with the coherence and cohesiveness within a given belief system. The agreement I'm referring to does exist across ancient and modern scripture accumulated over millennia within a particular belief system... namely mine. If this were not the case, I wouldn't be believing it would I?
So you have a community that has insisted that its members hold particular views and kicks out people and ideas that disagree? No wonder it has "cohesive agreement". It's no more surprising than finding a lot of Pontiac fans in a GTO owner's club.