Your argument is a non-sequitur.

The original argument was that there was no point in investing, because if you'd invested 10-15 years ago, you'd have made a lot of money. That argument is wrong for obvious reasons, which I will spell out anyway; just because something did well in the past is no reason to think you'll lose money on it in the future.

Your argument is that if you invest in something and it goes down in value, you lose money. That's true but not relevant.

Eli's point seems to be that it's possible to make money on an investment after it's had an explosive growth stage; the obvious truth in counter to the initial falsehood, and in no way addressed by your comment.