I wanted to prove that Faust can be defeated without using Legend gear and without excessive grinding... so here we are. I came here straight after getting to Zenebatos, so my levels are relatively low and as you can see, you don't even need recovery items if you play your cards right.
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Faust has 3 main stages, where he uses an 'Ultimate' version of magic at each one... living through these is really the key to victory. He also counter-attacks any damage with a spell of the attacker's element (which means you'll want to use DG armor) and at least 1 other random spell... so damage can rack up pretty quickly.
He'll start off with an Ultimate Fire-elemental, which you'll want to guard against. Pretty easy when you have Albert's HP as high as mine and the Red-Eye Stone on Meru. You may have to reset a time or two if Faust gets the first strike.
At half HP, you'll have to be ready for the Ultimate Water-elemental, which will completely destroy Dart unless he's in Dragoon form. Rose Storm helped immensely too.
At quarter HP, he lets the Ultimate Wind-elemental rip (kehehe). Shouldn't have many problems with that either as long as you have Rose Storm active.
Overall, as long as you have Meru healing every turn and keep Rose Storm up, it's really not all that difficult. My order of turns was slightly out of sync though, I'd recommend using something besides Magical Greaves to slow Meru down a little.