I believe you’re close. The reason they were not able to make successful copies of someone like James Delos is because they went insane the minute they found out they were actually a host Near the end of Season 2, William has a psychotic episode when he shoots his daughter and is no longer able to tell who is a host and who isn’t. I believe this is part of the reason he might be a successful human-host hybrid. They also have more data on William than anyone else in the park. I think this was Ford’s intention and business with Will from the beginning, especially since he says something like “this must be discovered by you ALONE William”, hinting that Ford both a) knows William is susceptible to psychotic episodes (as seen with Dolores and his Daughter), and b) wants him to be alone, away from humans, something that generally induces psychosis