The real challenge is taking someone’s STL, importing it into Fusion 360, and modifying it. Some models, while still printable, have mistakes that make it so that you can’t modify them easily.
Fusion 360 has an internal format that’s somewhere between its native format and a mesh, which gives you the capability to do certain things you could do in a native design, but not all. “Broken” meshes can only be converted to this intermediate format. I’ve come to rely on Meshmixer to fix most things that prevent Fusion 360 from converting it to a purely native object, but it’s not infallible. Even when a mesh is fully convertible, things like curved edges defined as multiple faces complicate the modification process. It’s then that I use a lot of offset construction planes and body separations to get cross-sections that I can extrude to fix some design issues, followed by Combine>Join operations to put the pieces back together. It’s those sorts of things that I wonder if I’m overcomplicating.