Is a web application just a big website?
No. Most definitely not. One is FAR larger, more complex and expensive than the other.
Web applications are browser rendered software managing complex data and functions at scale with a high degree of security, speed and uptime. Though web application complexity varies sharply depending on the specific system, they must be executed like the software they are.
But ... they look like a website.
It's similar to the house sized dump trucks found in strip mines around the world. They look exactly like any other dump truck you might see on the road … except they're huge and work completely differently. At that size and stress, the mechanical concepts that get you to work every day simply don’t work. Instead, they have a massive generator powering electric motor attached to each wheel. Even their brakes require a unique approach, producing so much heat that each must be sealed and liquid cooled. Everything about them is specific to the task of moving tons of dirt in a single load. They are a marvel of engineering and are unbelievably expensive.
But ... they look like a dump truck.
Scaling anything requires a fundamental change in how it functions - requiring bigger and more costly answers to questions that used to be simple when small. Scaling up is expensive, but building something too small to do the job is far more costly.
The web is no exception.
Want to make a good first impression? Pay attention to your homepage (your users already are!). Here are some tips for great homepage design.
How do you make a minimum viable product that gets all parties' buy-in? You prototype. See why prototypes are a required step in app design.