No, you go grind for a few hours and upgrade your weapons which have no restrictions and only penalize your score. It's how I beat the few bosses that did give me issues. Grinding still exists in the game, it's just your gear that requires it more than your characters.
Honestly XIII isn't terribly hard and I feel it has more fake difficulty than legitimate difficulty. My few deaths in the game largely came from the game abusing the "kill the party leader to win" mechanic the game used.
I'm pretty sure he's talking about how gear affects your stats. Basically all but the most lightweight of gear reduces the power of magic, so in order to build a great mage, they kind of need to be naked and unarmed to get the most damage out of magic. The game never tells you this and it's difficult to notice if you're not really observing damage changes.