The basic prerogative of a sophisticated bot is to ensure you believe that.

Having written a variety of sophisticated bots - some from pre-existing libraries, others from scratch; for specific websites and for general purpose - I'm reasonably confident most people who think they've never seen a sophisticated bot are mistaken.

I agree with you that anything more sophisticated or bespoke than a mass-spam bot is rare. But rare things happen often to most websites with nontrivial traffic. The types of bots with the most funding and skill behind them are the ones which don't try to spam anything on a website at all.