First of all, they're not my fantasy conspirators as you falsely state. There were conspirators because there was a conspiracy based on the evidence.
To answer your very long question simply -- that ridiculous scenario was better than admitting that LHO received a ride since that would show that he had people working with him.
Caprio has repeatedly claimed there was a conspiracy and the purpose of faking Oswald's presence on the bus was to cover up Oswald having gotten a ride from someone else. He apparently now realizes that makes no sense because a fake bus ride does not explain how Oswald got to his boardinghouse because the bus took him nowhere and the "fake" cab ride would have sufficed for that purpose. Now he is running away. Dishonest John apparently knows this as well. Here are the options:
1) Oswald was on the bus and received the transfer as the WC indicated.
2) Oswald was not on the bus and the bus transfer was planted on him by either a conspirator or the police to make it appear that he had been on the bus.
If you reject option 1 (as Caprio clearly does), then option 2 is by implication what is being suggesting. And that brings me to the question that I have repeated multiple times without a sensible response. Why would a conspirator or the authorities fake Oswald's presence on a bus that takes him nowhere? It advances no apparent purpose for the conspirators or police and entails considerable risk. So why claim he was on the bus and plant evidence to support this claim? Again, if the bus ride was to explain how Oswald reached his boarding house and cover up assistance from someone else, the bus ride does not do that. It serves no purpose because it took Oswald nowhere and the cab ride would suffice for that purpose. As a result, a faked bus ride makes no sense as part of any plan to frame Oswald or cover up a conspiracy.