Overall income potential: Excellent – Although it’s very possible to make $0 with a niche site if it doesn’t receive traffic, you can also make a lot of money if you rank well for good keywords. It’s not likely that you’ll make a living off one site, but they are generally easy to build. If you can build one successfully, you can probably build several more.
Don't mistake passive income with zero work. It's still work, it's just that your income is not directly tied to the hours worked. Anyone who owns rental properties knows that it's considered passive income but there is quite a bit of work involved. The work is front heavy but if you are lucky, you can collect rental checks without incident for many months before having to do work.
An obvious example is over exposure to bank stocks, which have been excellent investments for over a century. Though a foundation of most portfolios, bank stocks do involve more risk at certain stages of the economic cycle than many realise. Being less exposed to bank shares in the last few months could have preserved some capital. So, a more diversified approach can help mitigate some of these risks.