This argument is silly, and honestly it seems the only real reason you're against Protect is because you're being told to use it.

You think dealing damage is more effective than healing? Then sack off the healer, bring a third DPS into the dungeon. See where that gets you. The only thing you're accomplishing by DPSing is knocking off a few seconds off a target's kill time at the absolute best - the kind of targets that pose absolutely no threat to the party anyway. With any monster that poses at least some form of threat, your damage would be laughably minimal, and you'd likely be focused on healing anyway - and in such cases added defence >>>> healer DPS. I assure you, no one is going to be the worse for wear because you didn't fling a Blizzard or a Stone at a mob.

Plus, your job as a healer is two-fold. There's the actual healing part, and then there's the mental side of things. Being a healer is about more than just flinging out a cure spell now and then, it's about giving your party members peace of mind that they're in good enough hands that they can focus on their own role without needing to worry about their health. Party members who have confidence in their healer perform a lot better, simply because they can go all out and do their job properly and know that someone has their back. And naturally, an effective tank/ DPS is far more useful (and thus quicker) in damage output than a DPSing healer. Healers who spend too much time DPSing, let health drop too low, or don't even appear bothered about casting basic buffs (no matter your reasoning) seem unfocused, lazy, unreliable and even amateurish, and I suspect that's why the tank left.