Building scalable design systems from the ground up is one of my favourite tasks, for example, the work I did for Hellocar. This is valuable to both the business and the product. By starting with the fundamentals I believe you can then build on those blocks making into a strong foundation on which you can create a design language that develops as it iterates.
The success or the failure of a product never comes down to if you have the best designer or best developer. What it comes down to is how the team works together and delivers the product. Also, I am not a big fan of waterfalls 🚿 ☹️
Getting something in front of users helps to validate ideas quickly and cheaply. It is vital for successful product development, but I also believe you should be bold and challenging to the users. A good example is the work I did for Cambridge Audio.