The definition of a bot could be problematic though. If a bot is merely automated posting, then virtually every company, news org, website, and anything else that uses automated posts is a "bot", and are those bad? I don't think so, those are useful. The problematic bots are basically automated trolls.
Troll bots increase "engagement" metrics by quite a bit, this is obvious to any person if you look at the automated bot replies to virtually any post from a news agency or anyone with a large twitter following. They also jump onto every hash tag or breaking news event spreading garbage. You'll find dozens of bots making absurd statements followed by bots responding to those bots, and clueless people arguing with the bots. Combine that with the endless seas of human trolls that also jump into everything, and those interactions probably make up a huge amount of usage of Twitter.
Twitter remains useful for scanning headlines and breaking news, but outside of that the service is a complete mess.