after testing on several boss fights, I find holy succor is not only great to use mid combo if its needed but it has the strongest enmity return then any of my other moves, only move that seems to rival its enmity pull is full party rampart.
to answer the op's question tho. 100t swing, when CC is spaming it, can be survived very easly by keeping a few abilities on rotation. i rely heavly on 3 but a 4th can be counted on if done timely. all these abilities need you to pay attention and not waste any on a 10t swing or swipe or 100t swipe, as those 3 abilities can be survived easly without any ability.

on the first 100t i will use ageious boon on the second i will use sentenal, on the third (if either ageious boon or sent is still on cool down I will use shield bash, I have had about a 75%-80% success rate on stuning and interupting CC mid 100t charge. this , if it lands would buy you plent of time for either Ageious boon or sentinal to cool down. in a "oh shit' situation i will start casting stone skin on myself as soon as i see 100t being to charge. probably the safest way to survive that fight is to have your whm with a itchy triger finger on the SS button soo to cast it on you when ever 100t procs. timeing is crucial when relying on SS but if done right its a realy easy way to bypass the issue 100t poses.