If I were to peg a time, its when they had many 3rd party applications that hooked into your feed. They killed the integrations off in favor of their own app because Advertising.

Personally before it enabled inline images which turned it into a firehose of reaction gifs.

I'm starting to fail to see the difference between 4chan and Twitter at this point. Twitter is just 4chan with avatars.

Pretty sure POTUS is not on 4chan, but I could be wrong.

Depends on how you use it. As far as I know, my local police service, train company etc aren't on 4chan