I can conjecture some things, though I can’t be 100% sure on either:

First, maybe it’s fanatics/fanboys that don’t like competition making their platform less relevant. Second, it’s paid actors complaining. Third, it’s robot accounts making posts. Fourth, as proposed in the OP, people are getting the wrong impression due to noisy and problematic bubbles. Fifth, people being scared of leaving their comfort zone. Sixth, a mix of either some or all the previous possibilities.

Blocking, yeah.

Putting the tone aside, I usually browse the All tab for that reason, and also because subscribing in Lemmy is weirder than it was on Kbin (even if it doesn’t crash the page like Kbin did). Nothing personal against the communities, and sure, it’s an exercise on patience, but after some time, the results become noticeable as my feed gets fine-tuned into what I want to see.

From the instances I used, it seems to be a mixed bag. Some even allowed for the user to block domains unrelated to the fediverse.

Was commenting more generally, in case there’s someone against Facebook in instances that don’t block them.

And about lemm.ee, although the guy running it is strongly against defederation, I guess Facebook the company is too much even for him. "<.<

Blocking everyone and every community you see from Facebook’s new parasite social media could be good, me thinks.

Unfamiliar with it, but in the regard of instances going down, specially after my previous main instance died with no signs of returning (again), if you find any interesting posts even on instances seemingly stable, I think it is a good idea to back up those pages. Personally, I would propose methods like Internet Archive’s Wayback Machine and its alternatives like Archive Today, the print to PDF option from browsers, and/or saving a given page as a MHTML bundle.