I've done my share of vibe coding, and I completely agree with OP.

You just don't build up the necessary mental model of what the code does when vibing, and so although you saved time generating the code, you lose all that anyway when you hit a tricky bug and have to spend time building up the mental model to figure out what's wrong.

And saying "oh just do all the planning up front" just doesn't work in the real world where requirements change every minute.

And if you ever see anyone using "accepted lines" as a metric for developer productivity/hours saved, take it with a grain of salt.