Garth'zel just keeps his arms folded across his chest and raises his eyebrows, waiting for Kylo to finish working his way through that line of thought. Although he'll add one bit.

"I'd like to point out my own Master--first Lord, then Darth--Zash had been manipulating me since before I was officially her apprentice. What she really wanted was a younger, healthier body to take over. So Masters doing or saying whatever they need to in order to get the results they want isn't exactly unheard of."