For me yes if your investment is small buying the safest is the best choice, you can only diversify if you have large funds I was faced with that scenario and it's not logical to diversify with a small amount so I picked Bitcoin and that's the best decision I've made, if I have diversified with a small amount I would have lost half of my investment, so I prefer the safest one which is Bitcoin, it will go down but it will eventually recover.
Bitcoin should have the largest bulk or the main coin in your portfolio.