It's my opinion, but I disagree about the least amount of work. I used to think that, but managing people alone is incredibly difficult. I met regularly with each person individually, we met twice weekly as a team, we all had different meetings we were involved in that had to be scheduled around. I had to continuously review their work, training, quality, quantity, etc. And then discuss it with them, provide effective feedback, and if they didn't improve - managing them out is itself a strenuous, long process. And that's the people side of managing. The other half is the strategizing, planning, program management, etc. The org I worked in is in a fairly dynamic field and during my tenure we had 2 big U.S. law changes that affected our entire process.

Now, delegation is KEY to getting work done and leaving time for strategizing, planning, managing, etc. so it can appear that maybe they're not working as much or doing as much. But their job just differs. That's all assuming they're not shitty managers. There are different types of managers - the ones who do nothing but looked busy, the ones who do work but didn't effectively manage/lead, the ones who do both, the ones who lead and don't do much work.

I unfortunately was in an organization that was heavily understaffed and had to do all the "brain work" with my VPs and executives, then turn around and manage all my people, and still do grunt work at the bottom from time to time.

After my experience, I think managing people - truly managing and leading them, not just ticking boxes/etc. - is a big job.