I'm going to preface this with the usual "I might be bad and have done something incorrect" disclaimer, since that's entirely possible.
I think that Warrior class could use some buffs through either more items or raw numbers. The main reason is that it feels like it kinda can't compete with the sheer capability of Black Mage. Warrior's tend to pick up strength/agi/toughness for their core stats, which leaves their mentals in a fairly piddly state, meaning that the bosses that deal tons and tons of tease damage will simply wreck a Warrior without mercy. Meanwhile on Black Mage you can kinda just pump willpower for your primary casting stat, end up with pretty good mental resist anyway, and then you can also wear the witches outfit for additional focus defense on top of that, meanwhile you're either nuking things before they have the option to really deal damage to you, or Cait is giving you hugs and bandaids every few turns so your health never really drops that low anyway.
So, trying to play as a warrior and wear heavy armor/big shields typically means you have negative initiative, alright physical resistance, and pretty dumpster mental resistance. Thus, a boss that deals tons of tease damage or heals through your gradual grind of damage (Hive bosses, as one example) will basically be a sudden wake-up call of "Your class is bad and you should feel bad". I experienced this personally where failing to be up-to-date on my saves lost me several hours of progress due to getting trapped in the beehive. Frustrated, I started a brand new save as a Black Mage and have basically easily won every fight since, especially when you get the famous/infamous grease + fireball combo.
But I don't think that Black Mage needs to be nerfed to bring it in line with the other classes, I think the other classes need to be a bit more practical/competitive in comparison to Black Mage. Charmer is also fairly useful due to it having an option to constantly heal tease damage and the stat preferences for the class typically enable your companions to contribute effectively. White Mage feels fairly niche in that it feels like you typically only see it used for party compositions where you neglect to bring Cait (and lets be real, who leaves the pink kitty at home? I'd be willing to bet next to no-one does.) and Thief feels alright once you get your massive crits rolling.
Meanwhile, Warrior just feels left behind. The power-set is fairly lackluster and you get kinda piddly items that stack negatives on you without a terribly great amount of benefit.
But, of course, I could be entirely wrong. If I am, I'm happy to be proven incorrect.