I disagree. I think it WAS a runaway speculative bubble that burst. But you're right, Bitcoin is seriously undervalued. It's just that when growth is too fast, we have to correct to a more reasonable level before continuing to grow.
While the term has negative connotations, all a "bubble" denotes is simply a period of expansion followed by a rapid contraction. One can determine that somewhat objectively by simply looking at a graph.
If this doesn't look like a rapid contraction to anyone, they need their eyes or their head examined:
I certainly wouldn't mind putting "bubble" in quotes, because the price of BTC generally settles far above where it was when the "bubble" started, but still well below the peak price, and generally slowly increases in price after that before another cycle.