I think you’re setting up a straw man.
The problem here is not that the you gave a what-by-when — the problem here is that you gave a what-by-when without factoring in all the other commitments on your plate.
In other words, you’re simply Doing It Wrong. You don’t need fancy techniques like holacracy, agile or GTD to avoid making such a mistake (although GTD is integral to my life) — you just need to never, ever make a commitment without considering your other commitments. Not exactly rocket science.