I think it depends on the website and forum, twitter and reddit are filled to the brim with bots and shills, particularly on popular political subs in reddit's case. The shift on r/politics from normie, but diverse, politics before the 2016 election to the most obnoxious democrat circlejerk on the internet was not organic, to say nothing of the reddit line on Ukraine. On twitter its known that most of the like are fake and paid for, or that bots accounts are used to repeat the same identical tweets on some special interest, or artificially inflate tweets that are in line with the agenda of whoever paid for the bots. Even when I made tweets critical of US foreign policy in some way I would have obvious bots like and retweet it.
On forums, including imageboards, and in threads here, certain types of discussion about certain contentious issues or conspiracy theories tend to draw an abnormal amount of posts clearly seeking to derail the thread in a variety of ways.
Dead internet theory is an exaggeration of the real issue of digital astroturfing and the corporate-intelligence state's goals of controlling the internet to prevent the masses from being more informed and organizing.