Now, if your goal is to get more Feat Points, then ignore this, as this will actually spend more.
BUT, if you want to do something about Entropy ONLY being used for the Life Drain Boon.
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You can look at the Boon Access Feat (or the modified one: here )
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You can look at Attribute Substitution 2 Feat
Both of the above options would allow you to drop your Attribute Points spent in Entropy and put them elsewhere for your character.
NOW, a Third option that would allow you to not spend anymore feat points is talking to your GM about having an item that gives you access to Life Drain. This would only cost WL 2 to have.
So say a Ring of Invigorating Energy. You would still have to roll to invoke the Boon on yourself, and sustain in with a Minor action, but it would allow you to not spend any points in Entropy.
You might be able to talk your GM into having it be Reliable, but limited to only being invoked on the wearer to drop it from WL 4 to WL 3 and then you would not need to roll for LIfe Drain, only Sustain the boon with a Minor Action each round.
I only use this feature before a fight and DM wants me to use DC 22 will to use it without harming me
I’m not sure why your DM is having you roll a DC 22 Will to not be harmed? Is this b/c you are doing it a long time before any fights, so you are needing to sustain the LIfe Drain boon over several hours?