I am in a work environment where I actually get to do hard shit for fun, learn a ton, and also "get stuff done" and my employer is happy.

For some of the stuff that has been done already, it might still make sense to do your own implementation, for example if you want to be able to experiment without having to navigate and learn a huge codebase and then have to maintain a fork just to have your own stuff in.

Another project we are starting now involves replacing software which is outright crappy and wastes our time. Thankfully my employer was able to see and understand this after talking it through with them.