I've been a manager. Managers burn out all the time. They're just not allowed to show it. They get some degree of exemption from the petty humiliations (time tracking, on-call duty) and they do have human shields to throw in front of a bus or few... but as a middle manager, you're even closer to the truly horrible people up top, and your daily life is consumed by the issues faced by your unluckiest subordinate (sometimes he deserves it, sometimes he doesn't). You don't spend time with your underlings when the work is going well; you're constantly being pulled to deal with the crises and the sad cases.

Every company has an invisible line, like the officer/enlisted distinction in militaries, but always undocumented for obvious reasons. Above it are the real humans whom the company cares about; below it are the "resources". ICs are always below the line, except in R&D jobs that aren't available without a top-10 PhD... but most managers are also below the line.

Above the line, you basically write your own performance review because the bosses are your buddies. Below the line, it's miserable, and as you said you're one delay or mistake away from being sent to the Performance Improvement Camps. Almost all first-level managers in a company of significant size (25+ people) are below the line and spend just as much time on humiliating work justification (e.g., status reports) as the guys at the bottom.