Echo chambers are not dependent on having an algorithmic feed. It just matters that the people you talk with and the information you consume, etc, filter out dissenting opinions from what you hold.
Lemmy is still very much an echo chamber simply by virtue of the people who tend to be here. But we can balance that with time spent on other platforms, IRL relationships, etc.
Iirc, when the ADL put out their guidance on Pepe, it was during the 2016 election when Pepe was being actively coopted by alt-rightera and neo Nazis. One of those "take something innocuous and poison it by using it as a pseudo secret signal to other bigots.
I vaguely recall them saying that Pepe was a hate symbol only insofar as it was being used for that purpose. I wonder if that changed, or if this investigation is ignoring that nuance to hamfist a "hate speech" argument.