There's "comfortably", and then there's "in style". I'm a big fan of the subreddit /r/financialindependence, which is about retiring early, and it's actually surprisingly (semi)-easy - your estimates are way too high. With really just a couple million, you could live off that pretty indefinitely if you did it smart. But while there's certainly diminishing returns after that, I'd say it tapers off pretty slowly - while being able to retire early at all is the biggest thing, I could easily increase my enjoyment of my retirement by splurging more and more, based on how much money I had, up to a point. Total rough ballpark, I don't think diminishing returns would start to make additional money *totally* pointless until probably around the 100m mark or so.
But yes, definitely at *some* point more money is irrelevant, regardless of specifically what point that is, if you're just talking about personal enjoyment of life. Jeff Bezos, however, probably thinks way bigger than that, or Amazon wouldn't have become such a monstrously enormous company in such a relatively short period of time.