Diversification is for people who don't know what to invest in. If you did your research and decided to put money into a project, it's because you know it will go up.
Otherwise, you're just a gambler, not an investor.
If having a 'portfolio' full of crap is your way of being a 'smart investor,' go ahead.
I think there is a sense in what you said. You are trying to make a point for putting investment in one single place but that you can't be sure of its success rate even though it is given that bitcoin won't crash. However, with such analysis of difference between gambling and investment, what is now the truism of not putting your eggs in one basket?
Therefore, despite the general saying that bitcoin is a good investment, we can also see some coins that we can diversify too. For example, dogecoin has done quite well lately and people who invested in it didn't regret it. Likewise Eth, binance and some few coins have also given some returns. At least you can have some margin profit by the corner while your bitcoin is still growing.