It all depends on how much you want to maximize your jobs.

Gladiator alone is good at mitigating non-TP attack dmg from mobs, but outside that it is fairly weak at building hate, dodging Special attacks, and dealing dmg with Glad only abilities.

Optimal would be: Listing a few big items you get that are usefull in different fights while tanking.
Mar 48 (Warmonger, disorient, defender II)
Pug 42 (taunt II, Feather Foot II, Accomplice)
Lnc 36 (Diversion)
Arc 36 (Decoy)
Thm 50 (Sac III, Siphon mp II, Emulate, Contagion)
Conj 48 (Cure III, Chainspell, Spirit Bind)

Now this is not all required to be successful but the more you have the better tank you will be. Most those above are only really good in longer fights (ogre/Batraal/World NMs). Outside those doing dmg and helping kill faster will be more beneficial, so using more DMG+ stuff would be help.

In the end like with almost all the jobs now, the more you level the better you get. That is really true when being faced with mobs that hit for over 900dmg a punch.