And that is how, through power creep, you not only get nerfed content and disproportion within each tank's kits (percentile sustain feeling increasingly less valuable except where uniquely preventing OHKOs, making their kits feel increasingly lop-sided or outright jank), but also role imbalance that makes healers, especially, feel like crap to play.
If there is an outlier, unless its direction would also improve the contexts of that role, it should simply be trimmed back or balanced more holistically (e.g., accounting for any healer GCDs saved and raid-positional opportunities afforded by taking the high-sustain-but-faintly-lower-damage tank over the lower-sustain-but-faintly-higher-damage tank). You shouldn't then just increase everything else to the outputs/affordances of that outlier.