Here is the hierarchy:
1-Yami Yami-Teach can steal and contain souls
2-Yomi Yomi- Brooke can control and manipulate souls
3-Death Death- Doc Q kills the soul
4-Heal Heal- Mansherry can heal people and restore inanimate objects completely(since its a non living things it takes more power)in exchange for sending a portion of her soul to Yomi
5-Ope Ope- Law can make a soul immortal in exchange for sending his soul into Yomi
Bonney’s fruit is in the middle as she can alter life spans in he extremes(making someone very young or very old). She can also do the same for objects which is why she has so much potential.
Since she can severely alter the lifespan of anything, her own life force is constantly decreasing. She eats so much because she has to in order to replenish her life force. If it runs out, she obviously dies. That’s why she was so impatient next meal in Sabody despite having some food left. She had no time to waste