So to first make that very clear: I do not consider the navigator to be too strong per se and would not have a problem with something that makes him better after the suggested change.
However, the navigator is totally fun draining for me. He completly counteracts the whole game design of having about at least 8 hours to react to everything (depending on sub speed and flying distance).
So what is my real problem with it: The possibility to change the direction at ANY time. Please for god's sake give it a cooldown or something like that. We play in private games and there is a wide range of amount of time spent and many of us check in maybe 4-6 times a day. A navigator which is completly unpredictable and only counterable by a pirate is just annoying as it forces you to watch it move every single step, as it could change direction at any time.
If a cooldown would make it too weak, buff it with something else, but please keep the ~8 hours of reaction time in the game (I am aware they are merely a farce, as it is very often about seconds/minutes especially with specialist-combos). However, the navigator is so extremly against this principle it makes me sad.