Steve Blank has one of the best definitions of what is a startup:
“a startup is an organization formed to search for a repeatable and scalable business model.”
To ensure that a business is scalable, the problem the startup builds a solution for should have a large addressable market.
An important aspect of it being a repeatable process is a function of how simple the solution is.
Thus the harder the problem and the simpler the solution, tends to make for businesses that achieve scale much faster. This does generalize other factors such as network efforts and available distribution platforms etc.
However at it’s crux I do believe simplifying your business to benchmarking how difficult the problem you are solving for is compared to the simplicity of the solution is a great way to quickly evaluate the viability of your startup.