It seems that the "Dismiss Fleet" capability for flying fleets does not function consistently. It is not available all the times, and I have not found any logic for it.
See attached image:
3 flights in expedition. Dismiss Fleet button is not always there.
2 flights defending objects. Dismiss Fleet button is not always there.
1 flight defending coordinates. Dismiss Fleet button is there.

A tutor's reward is to see his pupils progressing and enjoying. Pupils are not vassals!

I am a tutor in real life, and I tend to honour my role even in the game.