If you're a team of one, either as a sole trader or as the only member of a team that deals with a specific discipline, how much can you really improve and grow?
In the context of a being a web developer, being a sole trader gives you a variety of projects and carte blanche to pick and choose the the appropriate stack. Being a web developer in a team of backend developers within a business organised to isolate team work streams leaves less opportunity to step into the unknown. This is compounded by all web work existing within a repo full of existing decisions on stack.
The biggest challenge in my job at the moment is in design. With no designer in the team and a wide range of stakeholders, users, and people within opinions that need to be placated, it's on me to put considers and high fidelity designs together. I suppose it's fortunate that this is part of my skillset despite it not being anywhere near my job description.