At least so far according to Cloudflare bots consist of around 1/4 of all internet traffic. But that could be pretty far off depending on how they get those estimates.
But what I'm curious about, whichever number is true, is whether people mean "malicious bots" when they say this, or just any kind of autonomous agent. And also whether they are counting volume of data or simply network requests.
Because if by "bot" they just mean "autonomous agent making a network request" then honestly I'm surprised the number isn't higher, and I don't think there's anything wrong with it. Every search crawler, every service detector, all the financial bots, every smart device (which is now every device) and a thousand other more or less legitimate uses.