Imagine if you could micro monks like this

Someone playing a song on an organ: https://www.youtube.com/watch?v=Nnuq9PXbywA&t=1m7s

He plays the same key every time with one hand, and plays different keys with another hand. Imagine you could select a different monk by pressing a key, and then move the cursor a small distance to select a target for that monk, obtaining unique targets for monks as quickly as this person plays the song.

This is not a 'select idle monk' hotkey. This would be a 'control only one unit in the current selection' hotkey. Pressing it again would move to the next unit in the current selection.

Monks would still have their weaknesses. Take a long time to convert scouts; RNG convert that sometimes takes the whole ~15 seconds; unable to convert siege weapons or towers without an expensive tech; unable to bash down a palisade wall with 2 HP; unable to do anything but run away when out of faith; unable to convert if the player does not notice an attacking force because their attention is distracted; unable to chase mobile units and respond quickly to raids.