I’m endlessly perplexed how a human with the same number of hours as me, can rule a kingdom, or run a modern country, or be CEO of a major company, meanwhile I’m working long hours every day and still get nothing accomplished.
Being a leader is a matter of taste. Make the decisions you need to make, take the actions you need to take, delegate the rest. If you had a very qualified group of people to do absolutely everything done you didn't want to do yourself "you" would get an incredible amount of stuff done.
Watch The West Wing for a taste of how the president of the US operates.
Another way to see it is they themselves don't get anything done, in the end others do all the work.
And that works very well even today when you are high enough to get a personal secretary. For the engineer who always shared the secretary with several others she didn't know you as well, and in any case their preferences were not important enough to consider (you don't get first class options).
Even for my boss, outlook is a force multiplier over a secretary because he (happens to be he today, has been she in the past, and likely will be again in a few years) doesn't have very many things where knowing preferences matter and doesn't have such complex scheduling needs that a human needs to do it. The ability to schedule his own meetings is much more powerful than asking someone to do it - while it might take more time to do it he can see that by not inviting one person the meeting can be had sooner and that is a much greater multiplier than the time saves by having someone else who not knowing those details delays the meeting until everyone can be there.
Yes when your situation is such that a secretary can "understand you, and act on your behalf in the matters you delegate, knowing what outcome you would choose yourself" it is a force multiplier. However most of us are not really that different from anyone else and even where we are we are not allowed the level of differentiation. We also don't have nearly the ability to delegate things, much less enough things that someone else can delegate them on our behalf. And so for most of us outlook is a force multiplier over the secretary we would get.
She typed his messages; that task is obviously done by the boss himself these days (Obama's blackberry addiction is a case in point). Voice-to-text handles her job while I'm driving; NO ONE did that job back then.
In the middle of the night, I can set an appointment that just occurred to me. Again, that's not something 1980s me could do.
Technology is a force multiplier you are ignoring. As bad as Outlook seems, it is better than most secretaries could be.
Note again that I'm using "she" intentionally. When females are considered unable to do "real work" we don't value their time and so it is a force multiplier for the men who don't have to sit on hold, and we ignore all of her time that is wasted. I agree with those who are glad such days are over.
Of course in 1950 we didn't have computers able to do many of the things assistants did. As such we needed them to manually do various tasks that today computers do better. However the sexist making it females who are doing the job harmed the better female who could have done something better, and also the less capable males who couldn't do anything more complex anyway. (though there are a lot of jobs that those males could do that are even less complex)