It's somewhat mythical that the "experts" got Trump and Brexit completely wrong. Fivethirtyeight, the most-famous among the poll aggregators, had Trump at 25% in their last prediction, for example.
That's not perfect, but they have literally written hundreds of articles trying to tell everyone that their predictions are just that, predictions. They also have an analysis showing that the polls were more accurate than in previous elections. That's not very helpful when +-0.5% can make all of the difference, but I'd expect HN of all places to have some appreciation for the concept of probabilities and uncertainty.
What's more important is that the experts got almost everything right in regard to, for example, the UK/EU negotiations. Which is why you can currently earn more money selling "Told you so!" t-shirts in Brussels than investing in Bitcoin.
But ultimately "is bitcoin a bubble?" isn't a popularity contest–it's a question of fact. It's the same as "is their any underlying value that makes a bitcoin worth $20,000?".
I'd argue the answer is almost certainly nope, because bitcoin has failed spectacularly at the mission it initially set out on. It is useless for transactions, as shown by $20 fees. It's far less secure than cash under your mattress. And it's not anonymous to any reasonable degree.
Basically all of bitcoin in active circulation is held for speculation, which sets it apart from other currencies. The only analogue is gold, and one could reasonably say that gold is in as much of a bubble as bitcoin. The only question remaining is if bitcoin can pull of becoming the second bubble-that-doesn't-pop.
It's not impossible. But my guess is the bubble pops as soon as BC stops being in the evening news every day. Take away the FOMO, and people will prefer a store of value they can touch.