As an airline pilot and FI, I have always had to work much harder as an FI than in any airliner. Hand flying decrepit old turboprops included, let alone "systems managment" in something a bit more modern!
Nope, an FI does work hard if they care, especially as the actual teaching is often only one of the many tasks they have to complete.
Some students are a joy and with them, the job becomes easy, but with others...... Let's just say you start to understand why some species of animal eat their own young!