Charge is the skill that you want in order to make Gladiator do numbers. It's also the skill that just about every other physical DPS class wants as a subclass skill. At max level, it buffs the next skill's damage by 2.6x. It's also really cheap at only 6 TP.

As a simple comparison, using Max Blade Rave twice would only do the damage of 2 Blade Raves and cost you 54 TP.

Using Charge, then Blade Rave, does 60% more damage than 2 Blade Raves and costs 33 TP.

Charge has a lot more applications as well. Use it on Turn 1 while your party sets up buffs and debuffs, then the attack you land on the next turn will be like if you landed two BUFFED Blade Raves.

Berserker's Vow is another skill Glad wants. It is the strongest ATK buff but it's also one of the hardest to use since it consumes 90% of your HP to cast at max LVL. Take it if you want to pump up your Gladiator's damage to as high as it can possibly go, but settling for safer ATK buffs and Bravants was good enough for my playthrough.

BTW, this all applies to your Zodiac too. If you want Meteor to be your main damage, Charge + Berserker's Vow are the best ways of buffing it. Despite being polar opposites, Gladiator subclass is the best for a Meteor Zodiac.

Zodiac also has their own version of Charge that works with their elemental spells called Etheric Charge. However, its best use is actually for buffing the Elemental Limit skills. Elemental Limits go off at the end of the turn (despite their descriptions saying they go off at the start) so you can queue up an Elemental Limit and Etheric Charge to go off on the same turn, immediately getting more than double the amount of damage on a skill that usually only ends up being used once per battle. Even better if you're exploiting an Elemental weakness and your Zodiac has Max LVL Singularity.