It's cheaper but not cheap
If you're building a variation of a CRUD web app, or aggregating data from some data source(s) into a chart or table, you're right. It's like magic. I never thought this type of work was particularly hard or expensive though.
I'm using frontier models and I've found if you're working on something that hasn't been done by 100,000 developers before you and published to stackoverflow and/or open source, the LLM becomes a helpful tool but requires a ton of guidance. Even the tests LLMs will write seem biased to pass rather than stress its code and find bugs.