In my experience, it's definitely faster to do manually if it's something that you know well. What LLMs enable is to skip research and learning by producing usable code immediately.

There is a long way between "usable code" and "the code I actually want". And each change I ask for piles on the slop. I don't get the slop when I just spend the same amount of time to write it out myself.

Most of what I find AI useful for is analyzing large volumes of data and summarizing, like looking in log files for a problem, or compiling reports from tons of JSON data. But even for those use cases, a simple CTRL-F is way way faster.