My general idea of how a dragon should function starts at Smaug vs. the entirety of Lonely Mountain dwarves, then Dale, and eventually Lake-town. It is clear that numbers alone cannot win against this sort of creature. And it is also said that Smaug was not the mightiest dragon to ever live, far from it. 5e does not represent the average dragon in a similar way.
So yes, I'd say that bounded accuracy is the wrong choice for not only epic level D&D, but level 13+ D&D even.
When we're talking about normal creatures that are perfectly killable by sticking them full of steel, like minotaurs or hill giants? Sure. When we're talking about old powerful dragons, demon generals and lords, high elemental forces? I'd disagree.
For me, it means that the setting doesn't need to have too many high-level threats. If there's a hundred ancient dragons out there, and most of them are malicious, then dealing with one is rather diminished compared to if there was only one or two, and having them be preoccupied enough to not cause problems until it's time for them to do so is also more plausible.