But I have never heard anyone famously say, as Dawkins said about Darwinism, that [endosymbiosis, gene transfer or neoteny] make it possible to be an intellectually fulfilled atheist.

Why not? Because it’s not clear that these processes could not be guided. The mechanisms are proposed simply as mechanisms by which significant changes might take place, not as mechanisms that rule out guidance.

“Darwinists” aren’t pointing to these specifically as making it possible to be an “intellectually fulfilled atheist” because these are details in the larger picture of evolution that allow such a thing. Claiming it for these specifics would be akin to claiming that genetic mutations make it possible to be an intellectually fulfilled atheist. Absolutely genetic mutations are a necessary component of evolution, but they on their own are not enough to make such a broad statement sensible. It’s the totality of evolution, both what is known and what is as yet unknown, that makes such intellectual fulfillment possible.