If you can't easily clear Rank 3, you'll have no chance in rank 4. Even the rank 4 trash is potentially lethal, though this varies by element. You need superb damage, excellent mitigation, or Gaia to clear the final boss regardless of element, because 1 Full Burst and a volley of skills / auto-attacks typically won't be enough to end Rage. That's before even considering the various things that can go wrong and derail an attempt, such as bad transitions (no debuffs ready) and Black Propaganda misses.