It's not hard to do those.

And I suppose for most business cases out there, writing data to the DB and reading it back later is all it takes.

However, there's plenty of other problems where the skillset you mentioned falls short.

For instance, you talked about designing a database schema. Do you know how to design and build a database itself from the ground up? What if that DB has to be distributed, with thousands of writers? How do you ensure consistency and consensus? (These are all solved problems).

Think about Linux kernel developers. Do you think DB schema design is an especially relevant skill for them to have?

Can you come up with a compiler, or your own programming language?

Try building your own text editor, with features like syntax highlighting, undo/redo etc (it takes clever algorithms).

I'm not claiming I can do all of that; just mentioning that the whole scene is much more interesting beyond the horizon.