People are just forgetting that having 150 tenacity more doesn’t mean that you won’t get debuffed. It means that you’ll decrease the chance of getting debuffed, not making it impossible.
If also means that Palp is giving 35% potency and that Sith are around 50% potency except maybe Vader and Sidious. That’s already 85%, with proper mods you can be 99% which would reduce the gap between ~180-200 tenacity.
That being said, my Palp is 88% potency and DN/Sion are 50% without working it that much and without gear 12 for the 2 last of them.