There is nothing wrong about any approach: like everything in life, it's a balancing act.
If you want something maintainable in the long run (5-10 years), it's probably not the best idea to start with that approach. But then again, you probably have no idea what direction you should be heading for the next 5-10 years, so it's not a big deal.
I know it's a bit conflicting advice, but that's the point. When you know exactly what you are building (which is seldom the case with web apps), you want to do it right from the get go. When you don't really know, it does not matter since a few years down the line, if successful as a product, you'll be refactoring heavily and probably doing it the right way at that point (iow, full tests come last).
If you want something maintainable in the long run (5-10 years), it's probably not the best idea to start with that approach. But then again, you probably have no idea what direction you should be heading for the next 5-10 years, so it's not a big deal.
I know it's a bit conflicting advice, but that's the point. When you know exactly what you are building (which is seldom the case with web apps), you want to do it right from the get go. When you don't really know, it does not matter since a few years down the line, if successful as a product, you'll be refactoring heavily and probably doing it the right way at that point (iow, full tests come last).