Indeed. Even when we diversify our portfolio when trading or investing, there are always a risks. Let's imagine we have $100 total in our port, but if we diversify it among 5 cryptocurrencies, you can only trade or invest $20 in each of them.
Consider that you didn't diversify your portfolio, that you just invested in Bitcoin, and that your stop loss is a fixed 20%. 20% of 100$ is $20.

Thus, losing $20 is so big. But, you will only lose $4 if you diversify your port among 5 cryptocurrencies.

This indicates that a risk still exists.
Nevertheless, one thing to keep in mind is that, in terms of cryptocurrency and from what I have observed, when BTC dips, alts will also follow.