Could my huge advantage in "potions" and "revives" ever help me win a battle?

While you cannot use revives and potions during fights like you can in the traditional Pokémon games, you need them to heal and revive your Pokémon after fighting at a gym. Any Pokémon hurt while training/defending at a friendly gym will need to be revived and healed before being used again, and any Pokémon who faints while fighting at an another teams gym will also need to be revived and healed to full. If a Pokémon is only hurt while attacking, it will only need to be healed and not revived.

It's not quite true that you must heal your mobs before deploying them against your own team's gym for training. The Pokemon that goes up will have the highest hp, then cp. Even wounded pokemons can be sent back in for training, I managed to burn through all of mine today in one mad push once I was out of winners - just out of pure curiosity. The lowbies will be transferred sooner or later anyway so no real need to heal them all, they can be transferred when they're at 1hp for the same value.

That said, you cannot station one of yours in the gym for defense unless it is 100%.