I guess for considering bitcoin as a bubble is quite reasonable. And so does for ethereum. Basically all cryptocurrency has the same type of movement, the can be consider as a bubble as well. However, the chance of the other altcoin to become a bubble is very low because the change of the price is in low frequency, it's very different if we compare it to bitcoin.
It is not only questionable, it is the exact opposite of a bubble...I was watching a documentary about the next financial crisis that will be caused by the endless amount of money printing in combination with record high depths...I believe it was on Youtube.
Someone wrote something like this in the comment section: Bitcoin is not a bubble, it is the pin