You’d be surprised My school did not teach anything about software design, but it actually taught me very little outside of what I already knew.
But back to the point.
You are exactly right, and yet most of the web frameworks in the wild steer you rather into low cohesion, multiple responsibility classes that, just look at rails models…
I have started to learn elixir about 2 days ago and now I have the same question on my mind. I’m not planning to use Phoenix. My web app needs grpc and I found very small number of online resources about using grpc with elixir. And I found one library which seems to be still at a very immature state. I really like elixir/Erlang and OTP though.