I disagree on two counts:

1. The market has seen no significant net increase in price, and is down significantly on recent (12 month) highs. So one may be early for this cycle (or at bottom). Alternatively, one may be late in the sense that there will be no further investment opportunities ever in the future, and that one would have needed to invest during a previous cycle:)

(This is see as evidence that it is not too late)

2. Markets act on fear and greed. As Buffett said, be "be greedy when others are fearful". Sentiment changes slowly, and heterogeneously (by which I mean different investors change their sentiment at different times and speeds). My observation is that most people are still fearful, but some are not, and the author of this article (and Buffett) are two such examples. So the logic "one person calls 'buy' -> no opportunity" does not hold for me. Now, if many (>=50%) are calling 'buy' then it is time to be fearful.. (This I see as rationale for why your statement isn't true, but not evidence)