In a measured test, with a skilled driver, who does the right thing for the entirety of the test, it is most likely that he or she will be more efficient with a manual transmission than with an automatic.
However, in real life, for real humans, over a longer period of time, the drivers with modern automatic transmissions will be more fuel efficient than drivers with similar cars and manual transmissions, because the automatic transmission is a reliable machine that will do the same thing, every time. It doesn't care if you had your morning coffee or not, if some asshole cut you off, or if you got distracted or bored or spaced out and forgot to change your gear to the right one.
And, disregarding the disruption the EVs will be, technology constantly improves, while human skill is fairly constant, so it was just inevitable that automatic transmissions would one day overtake manual transmissions in terms of speed and efficiency. Arguing otherwise is just irrational nostalgia.