What you're saying is technically correct, but misses the point. I also find it useful to draw lines-and-boxes sometimes, but it's much faster and more creative if you don't constrain yourself to a standard like UML. The only reason to use UML in this case is if you intend to use your diagrams as a communication tool rather than just a thinking tool.

But, as a single founder, you should have no need to communicate the kind of information conveyed by a UML diagram. If you require that much hand-holding, you're not ready to be a single founder. Time is a very limited resource for a single founder, and if you're spending time discussing UML diagrams, where are you going to find time to talk to customers, create a good marketing pitch, and all the other things required to create a profitable company?