Benedict Evans nails it:
But for an actual brand, developer or publisher wondering if they should do an app or a website, I generally answer that the calculation is much simpler and less technical:
Do people want to put your icon on their home screen?
Do you have the kind of relationship, and proposition, that people will want to engage with it enough to put your icon on their phone? If the answer to this is yes, then you should have an app – if only because the app store is the way to do that that people understand, and they’ll look for you in the app store. Once that app is there, you can leverage all the interesting and sophisticated things that you might do with it, or you might manage the flow of information just like your website, but the app has to be there.
And, he adds:
In either of these cases – whether you have an app and a website or just a website, you should presume that your customers will engage with you only on mobile.