I don't think that anybody should invest at so bullish market. Buy low, sell high. And there is a probability that we are at the high right now.
Other than buy low, sell high, this comment is not logical. There is a probability that ETH is at the high right now, but chances are it will go higher in the future. Relatively speaking, when BTC was at $600 it was low. So, even now, purchasing ETH now is likely to be profitable, unless you can produce a good reason why it will tank and not recover.