IMHO, the reasons mentioned are not very convincing. Your goal, when starting a product, is to find whether you serve a real user need or not. So, start with a website or a mobile app depending on what suits your users needs better. Where would a user naturally go (web or mobile) for that need? That's the platform you start with.
Having said all that, I agree that for many simple apps the better user experience, in-app, isn't that much different except in one major way: discover and re-discovery later. When you install an app on your phone, there is a nice big button on your screen at all times so you can come back to it. Getting people to install is hard but once they have it is way way better discovery experience than a web app. Adding a link to your desktop still feels pretty janky (right or wrong) to most people and most people don't know how to do that.