I disagree it was a mistake for the same reason I don't feel I made mistakes with unpredictable CHIPS. And this can be applied to most peoples "mistakes" or "regrets".
Seeing something in hindsight does not necessarily mean the original decision was a mistake, as long as it was a logical and calculated decision with the only info available at the time.
Buying "potential" CHIPS is a risk as their spilling into all kinds of TLDs was and still is always a fairly high risk with potential for a loss. No-one can really say if a certain TLD is the next bubble, or how high prices will rise.
So it's mostly a risk either way - Either buy early at high risk they become tradeable at all; Or wait to see a trend forming and buy at a higher price which is then a risk in getting ROI.
So yes you would have made a good ROI, but you could have lost a fair bit too. Given the risk factor, it's not a mistake just simply a decision to not take a risk. I think this is just good business sense TBH. Risk are needed in domaining, but calculated risks not pure gambles.