Dungeons in duty finder tend not to go as planned.
I don't care about efficiency. What I do care about is being prepared for the unexpected, something that's a given when you're playing with people you know nothing about.
50% for the tank is EXTREMELY concerning. All it takes is the right sequence of attacks and it's a wipe, plain and simple. Spells like Benediction and Excogitation are specifically designed as emergency skills; they aren't a crutch, and you should never abuse them as such.
Willful negligence is still negligence. I also don't think it was synergy when BOTH healers when I was tanking the trash monster in Alex and both let me burn on a boss that doesn't even do much damage today. Regardless, I don't think a level 15 THM alt really has any room to give people advice on healing.
Regen + shields + buffs and precasting. I'm not saying that you'll never use them (everyone does and should as-needed), but they're not option #1, either.