Keep in mind you can always block communities you're not interested in to prevent them from appearing in any feed. I've already blocked plenty of communities to make the "All" post list digestable.
There are so many though. I'm trying to prune politics from my feed but people keep making new goddamn communities - a dozen isn't enough, apparently - and then crossposting everything everywhere anyway.
Why would I? The list of communities which one wants to block is very personal / individual. My preferences what I don't want to engage with is purely mine and cannot be transferred to all other users. So any user should make their own decisions what communities they want to block, instead of blindly copying someone elses and potentially missing out on content they would enjoy.
I agree with you to an extent, but I think there should still be a default list of blocked instances that we could provide to new joiners, so that they can at least have a base to avoid the experience OP had.
Of course that would be opt-in, but at least that would ease the adoption a bit.