A senior developer won't need Rubocop, it's a blocker rather than an improvement. In the rare occurrence where you have an undisciplined senior developer, it's worth exploring training or re-evaluating the standards in place.

All in all, I keep thinking this is a problem of culture, if it's addressed there the value in Rubocop decreases drammatically.

That being said, Elixir formatter is "ok-ish". I didn't have the same problem with it because it doesn't overstep the boundaries of styling. It did remove valuable structure of the code for the sake of formatting standardization, so again it's actually doing damage, but at least it doesn't force you to write code that is more cryptic to a human for the purpose of pleasing a machine.