Indeed, according to METR, Mythos only achieved an 80% success rate with 3 hour tasks.
https://metr.org/time-horizons/
It fails all the time - as in it ends up doing something I want to change.
But this doesn't actually matter - if it takes 3 or 4 iterations on something that would have taken me a week it might be a day of human work, but it's still 5 times better than doing it by hand.
Play some holdem folks and keep track of how many times you lost with pocket aces.