Re: No worse than something on a web page
The strength of the blockchain by being decentralized and immutable. i.e. once something gets written to it - it can never be deleted and cannot be modified. This is why you can be sure a bot will always find its CnC server and the data being posted by it will not be modified.
Other CnC methods all have some governance over them. web page can be take down by the ISP, facebook page owned by facebook and they will take it down if abuse is reported. even the NTP server can be blocked since it has a specific IP address.
Regarding the public part, then yes, everybody can read what is written on the blockchain, but this is where encryption comes into place.
You can read more about it at the git page for the project: https://github.com/platdrag/UnblockableChains