I think a good case can be made that the biggest currencies like BTC and ETH arent in a bubble even though they could well be a bit overheated and due for a pullback.
Where you see the bubble is in the currencies that are nothing more than a coin thrown up with no basis for interest other than it is a cyrptocurrency. To equate it to the dotcom era, it is akin to all those who invested in anything that had .com in it, regardless of anything else.
Of course, the thing about bubbles is they can go on for a while before they ultimately popped. I know people who saw the housing bubble in 2003, one that didnt bust until 2006.