Fencer/Archer is horrid. No where near fast enough. Speed is not only one of the game's most important stats, it is also one of the Viera specialties. Assassin is the fastest job in the game (not including Tonberries), and has awesome other stats as well. It's easily the best Viera class for training.

You're right though. If you want a magic using Moogle, Black Mage and Time Mage work well. Similarly, Blue Mage is good if you want a magic using Human.