I believe that resurrecting Mortals is easier to do then Supernaturals.
Humans- Emily by herself has been able to resurrect Jeremy by herself and create rings then can limitlessely resurrect and human owner. And she only required her magic and no one elses. But they were only humans.
Supernaturals- Clearly this is another story. All attempts except for jeremy's(who was a supernatural hunter) at Bonnie's hand were unsuccessful. Luka, Kaitlin's son both failed. Jonas did not have enough power and Kaitlin( who's son was probably supernatural cuz of her) couldn't control it. Bonnie was the only one able to revive someone as she had both massive power and control. Though she died as nature struck back.
Humans have shown to be resurrected with very small amounts of magic. A supernatural who has died can only be revived with huge amounts of power. This explains why Emily could revive Jeremy earlier and easier in the show but Bonnie could not when he became supernatural.
The show bases itself a lot of Buffy. And they had something similar where People who died normal deaths could not be revived while supernatural deaths could be. So they were probably trying ot mimic that idea but do something that was kinda opposite.