First, not rude at all, you make a good point, but my point is, if OP wants to monetize it / make it a business, my unsolicited tip (not that I am some startup

First, not rude at all, you make a good point, but my point is, if OP wants to monetize it / make it a business, my unsolicited tip (not that I am some startup guru or anything, just a armchair wannabe) is that even though you go for a niche, you can bring in verticals adjacent to your niche, instead of just fitting a product to the market, you can actually generate new demand by expanding the market. E.g. The chances to convert a keyboardist who can play into becoming a synth head and therefore potentially a paid user are higher than let's say a doctor, so if you already have a musician visit your niche synth website, give them a link, maybe they'll get hooked and you gained a new customer.