Lots of people can write an app. At the end of the day you either have to get lucky with organic traction or be a little less lucky but be a relatively skilled marketer that has a good command of how to convert paid traffic.
I think this totally depends on the app, and the problem domain. CRUD apps? Sure, those have very low barrier to entry. But they aren't the only type of app out there.
You could argue that in a lot of domains you barely even need an app at all that requires more than wiring up google sheets to zapier or some such if you can cleverly package it up and target the right audience with it.
SaaS products are merely an exercise in problem solving for people/businesses and there's a lot of ways you can usually solve these sorts of problems without needing to be super technical with it. At that point your bottleneck will always end up being acquiring and converting traffic.