Well, during the mortgage crisis, very few economists would actually claim it was a bubble. Perhaps it was 5% - 10%. At least this was what appeared in the news. The big shots at the central banks didn't see this bubble either, for the most part. But now every big banker is saying Bitcoin is a bubble.
For the dot-com bubble it was much the same. The majority of people (economists, bankers and the like) that should recognise a bubble were only able to call it a bubble in hindsight.
The more I hear this is a bubble, the more of my spare money I will invest into cryptos.