The Demon Wall fight is not all that hard at all. It sounds more like you've ran into a string of bad luck than anything else. I've ran this several times with people only geared in AF and Wanderer's Palace gear and the fight is still quite doable. At that gear level, the gnats are a real threat but the wall shouldn't be. Typically, at the gear level I stated, people will defeat the wall when it is one repel away from locking people in the poison field. Which, to me, is normal and not panic worthy.

If you are running with people of that gear level or better and they still cannot defeat the wall, then it sounds like you are running with people who don't know how to maximize the damage of their class. This can happen a lot as people fall into a rotation they think is good but is actually sub-optimal and cripples their own damage.

As the pld tank of your runs, all I can suggest is going sword oath and helping your dps along as best as possible. Afterall, there's no risk in that since Demon Wall doesn't care about threat generation. However, if you're over geared, then you can simply tank both gnats and tell your dps to focus on the wall till the battle is over. That should also alleviate your troubles.

In the end though, I don't think a tweak is needed. It is a very generous dps race fight.