monk optimisation

[Allyrion]

From what I read here before that using DK after PB applies te buff and rebuff. So why use it last on the PB phase?

I'm 100% sure what you read about DK applying the buff after PB is wrong. Can't see to find where that was said either.
After PB, you are stance-less and your DK doesn't apply the debuff. This is easy to test.
So yea, that's why.