Rather than just discussing things and debating, I've decided to make a math tool. Here you go, a calculator for Leech Efficiency so you can stop wasting so much slots and stat rolls on needless leech!
https://docs.google.com/spreadsheets/d/1T46PW7-sD52o2uub2l-stRAu4a1UwHMYit0E9wZTq2s/edit?usp=sharing