If they wanted to nerf the Guardian's self-heals, Prey on the Weak was the way to go (though if they had, red-line Guardians wouldn't have been able to survive much before dying because their dps is so bad). It operates randomly and leads to some strange situations. Thrill of Battle was fine because it at least depended on using certain skills that define the Guardian, the response skills, and it was never the source of most healing. You could chain parry response skills in a strategic fashion to maximize their healing potential. With POTW a lot of it is just using Sweeping Cut.
Landroval: Tolvat (120 Guardian), Gelldir (115 Warden), Gloravon (115 Captain), Curwe (115 Champion), Glamdir (115 Rune-keeper)