I'd just recommend
starting from a tank perspective rather than worrying
first and foremost about (typal) output. Trim the things that --by taking up X% of the tank's sustain while being, themselves, uninteresting or carrying less agency / skill expression-- make tanking on those jobs that much less fun.
Thereafter, just make sure that their kits both seem worthwhile and competitive in situations both with low and high damage intake.
Once that's done, if tank sustain
still seems excessive, don't specifically target any particular type of sustain for reduction (flat or percentile, preemptive or reactive), but just rein things back bit by bit
as a whole -- thereby still keeping that kit's parts in balance against each other.
Too much of that sustain coming from percentile tools makes the kit lack apparently relevance when incoming damage is low. Too much coming from flat tools makes it feel less relevant when damage is high. Let the fun of the kit and basic parity/functionality determine the proportions of those tools in the tank's kit, and then just roll the excess back together.