Oh no. Why he was almost fired is a different set of problems from why he didn't wind up behind the camera.
Why Garret wasn't allowed/asked to direct is because he left as soon as his shooting was finished.
The rest of the cast that had directing jobs on Voyager, stayed on their own time, helped out and learnt the fundamentals and here's the biggy "They asked if they could direct."
I think it all comes down to the same thing regardless of exact reasons given. Attitude, commitment, professionalism. However you want to put it, he just wasn't leadership material.