I have ghost rider as a 5* at rank 3 and I had also put an mystic gem on him. Honestly he'll get you through act 5 but beyond that his damage output is average at best and won't cut it. In my opinion he's great in AQ for saving a ton of potions and I'd consider taking him to rank 3 at best. Beyond that his lack of damage won't justify his rank up.
As for his awakening ability he does benefit from it due to increased duration of buffs / debuffs . The fury which you gain won't make a difference to his attack unless he's at high sig.
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As for his awakening ability he does benefit from it due to increased duration of buffs / debuffs . The fury which you gain won't make a difference to his attack unless he's at high sig.