Not a mistake. Making an app that fits this niche might be how you differentiate yourself in the market and succeed as a solo developer. It'll let you grow at a slower pace, making it easier to iterate the app over time as you see fit. You could always offer an add-on service in the form of a subscription in the future.

I run a productivity desktop app by myself and have been doing it full time since 2017. The app is a one time payment, free support, no gimmicks, no marketing. Support is becoming time consuming, but profit is high enough that I may hire a few people to help soon.

Good luck! High growth rates with investors is one way to do things, but not the only way.