App is one of those dimensionless words like thing or object. “I built this cool app last night over a couple beers!” or “Microsoft is proud to release the 27th major version of the Microsoft Word app”, built with a 100 engineer team embedded in a 3000 person org to a billion users.
I tend to be an engineering and architect fanatic, but for that overnight app, creativity and insight is way more important than engineering or architecture. That overnight app is mostly composed of a preexisting stack of well-architected systems and libraries with just a little bit of local dev-written code. The amazing performance of the systems the app runs on will smooth over all but the most egregious performance errors. And if it has value but is really badly designed, rewriting it is often faster than fixing it.
But somewhere along the line from “overnight hack” to “aging monolith”, things get complicated and sticky. The issues that arise fairly quickly along the way end up being very similar to issues that you see with much larger apps.