Yes, it requires prior understanding of what you're attempting to do. That's more or less what I meant by "making your own brain work more" - if you treat it as an input for your brain to operate on and exercise your knowledge, it can boost your productivity. If you treat it as a tool that lets you think less, you end up with nothing but slop. Sometimes even slop will be useful, but the contexts where this is true are limited.
I have no doubt that agents will become meaningfully useful for some things at some point. This just hasn't really happened yet, aside of the really simple stuff perhaps.
Implementation plans, intermediate bot/hunan review to control for complexity, convention adherence, actual task completion, then provide guidance, manage the context and a ton of other things to cage and harness the agent.
Then, what it produces, it almost passes the sniff test. Add further bot and human code review, and we've got something that passes muster.
The siren song of "just do it/fix it" is hard to avoid sometimes, especially as deadlines loom, but that way lies pain. Not a problem for a quick prototype or something throwaway (and OP is right, that that works at all is nothing short of marvelous), but to create output to be used in long term maintainable software a lot has to happen, and even that it's sometimes a crap shoot.
But why not do it by hand then? To me it still accelerates and opens up the possibility space tremendously.
Overall I'm bullish on agents improving past the current necessary operator-driven handholding sooner than later. Right now we have the largest collection of developer agent RL data ever, all the labs sucking up that juicy dev data. I think that will improve today's tooling tremendously.