As being prompted by in-game support, I will post the question here and it would be great if any of the developers can share their official opinion on this.

There has been a discussion that people have tested out combined mitigation debuffs from a couple of different classes and brought a raid boss's (e.g. Shelob) mitigations down to absolute zero (up from approx 52% estimated) , in the sense that by applying any further (and there are available) mitigation debuffs would bring no merit to the dps.

If the devs can please explain if this is i) feasible and ii) working as intended. Thank you very much in advance.