Project 2025 is not a response plan. It's also not the same as the Republican platform. They publish separate documents. What you are seeing is the overlap between Project 2025 and Agenda 47. There are multiple think tanks for both sides that are not officially party affiliated - Heritage Foundation, Third Way, Center for American Progress, etc.

Most of the actual strategic mechanisms for either side will not be published. Why would you publish your playbook for the other side to anticipate your moves?

What happens is a candidate posts their platform, such as Ageneda 47. Then you can view the published documents from the think tanks on how that might be achieved, such as Project 2025. And yes, oftentimes the people creating or pushing those programs get put in charge of them or advising on them (see Biden pulling someone from the Center for American Progress to be an advisor, etc).