For a minute there I thought this thread was about me.

I have a similar story where I was playing on Black Mage and using Physick to heal because I was not satisfied with the way the White Mage in my party was healing.
I got yelled at because of it. Was almost an argument, but completely 1 sided as I just decided to ignore the person. The other 2 people in the party were silent and didn't seem to care either way. This continued on for most of the dungeon until the tank accidentally pulled a little too much and I said to myself "alright then let's see what you can do" and stopped healing. I didn't write that out of course, but that's what I was thinking to myself. Of course, the tank died, and then the healer died too, but I managed to clear the group with the other DPS with some well timed Sleeps and Physicks.

I couldn't help myself but chime in with a "You can handle the healing yourself, hm?". I couldn't help it, I was being flamed for the last 15-20 minutes. After that the healer left.
This was a cool story, bro.

What's the whole point? Well, you can't force your playstyle onto others, any more then they can force their playstyles onto you. Unless someone is doing something that severely impacts your chances of successfully completing the duty, you might want to just leave them alone. Suggestions won't hurt if you make them politely, but just remember that you can't force them to do what you want. Most people don't like being told what to do. After all, who died and made you captain? Personally I've started using the word "consider" a lot, as in, "consider healer lb" or "consider playing mage's ballad". That way I can truthfully say I've done my part in suggesting a better way without seeming like I'm taking charge and being rude.

In the end it shouldn't matter to you if a DPS is overhealing. As a Scholar, you are probably able to solo the entire dungeon by yourself. Just look on the bright side, if they are healing for a lot, you have to do it less, and you can DPS to your heart's content. That 4th person is not even necessary to have there, so you can just imagine being down a person. You can still complete the duty.