Help with Managing my Team

Hi coaches… I am a manager of a department in our company. Would like to have your thoughts on this:

Where would you draw the line between believing that your subordinate can still improve in their performance to have more output/result vs accepting reality that this is the limit of their capacity?

This is related to identifying if we need more people in our team. I have this thought that they should be able to do more than what their current output is since i was able to do so when i was doing it solo before. So i want to believe they can do better. But when i talk to them, they frequently says that their overloaded.

Can you help with some questions i can ask myself to help me determine which is which? Or on how i should manage my mind about this?

How does Brooke able to bring out the best in her coaches like you who helps us scholars so much?

You’re all very much appreciated!