Its probably more accurate for me to say that I think there is a gradient of people between instances. Using politics as an example, and without details, people seem to gravitate to instances where they are with like-minded folk. Combine that with local or global filter preferences, and echo chambers start to form on a per-instance basis. Communities of higher interest will likely be on the users home instance, after all.

But yeah, I am fairly sure most of us browse /all and see content from all over Lemmy. We still mix and mingle, but are still lightly bound by our own filter preferences. See above paragraph.)

(I am not trying to dictate hard rules of behavior, btw. Lemmy is too diverse for anything definitive.)

Personally, I try to only block specific communities and not entire instances. That has seemed to keep my personal feeds fairly open.