Sorry, I was quite sloppy in my previous comment. Agent B certainly can learn everything that A learns from the same observations.

What I meant is that you cannot learn from "general" observational data, unless it is structured in a certain way (the randomized controlled trial mentioned in a sibling). RL is able to gather data on its own, while other ML methods must do with what they are given. This means that RL could eventually discover the causal relationships, while non-RL cannot (except if the data comes from a RCT).