Gladiator/Thaumaturge would most definately not do this job justice as is. Red Mage most certainly needs the introduction of a new class, scout or fencer or what ever. Musketeer is a no no, we do not need to make red mage into a ranged backline job. So how do you make a jack of a trades? I have a very good example of red mage in my speculation guide but I'll give you all the short version here.

Scout Class - Weapon: Light Swords (Daggers, Rapiers, Katana) - Stealth, DPS, Enfeebles

The scout class opens up the best possiblity for red mage as it will have enfeebles right on it. I do not advocate making red mage some kind of enfeeble whore but hear me out. Now that your melee and enfeebles are covered you are free to borrow defensive and offensive magics from what even conjurer, thaumaturge, or possibly arcanist has to offer. Since the defensive and offensive magic are sub abilities, Red mage will innately never reach the strongest teir of offensive and defensive magic but will also have a variety of choices.