The gameplay option to remove knockback already exists in other content like PotD, the icons are known by players from o4s also.


But question really is if we need those diminishing returns on knockback/pullin effects.
You play as a tank and I can imagine melee aswell will encounter the problems, but they at least have a gap closer. As for me playing healer, I hate it more that the pull-in effects vary in strength, some take some seconds to stop your character moving (and you are able to cast again), some times the same skill pull in effect ends pretty fast and you don't waste much time in the process. So it is always different.
A very long effect might be if you are getting pulled with holmgang, but there is an obstacle like a curved wall between you and the warrior, the system tries to pull you to the warrior in baby steps around the wall(which doesn't really work out but takes a lot of time).
Compare it to the pve rescue skill for healers, which is superfast from start to end.

I wouldn't really want holmgang to be affected by this resistance buff in the first place, the problem is I am not sure if they can differ between fluidaura/drk pull/mch knockback from it. As dragoons can already elusive jump it, while the jump is only supposed to remove weight and bind...

Unmend has 30s cooldown, fluid aura 20s, blank 10s. So that scenario where you get hit by 2 or 3 of these effects is rare by nature. You wont have the "increase resistance" trait as tank so you are looking at 7-8s debuff resist without it and for healers like 15s with it, which sounds a bit unnecessary.
Other cc skills need that protection because the cc skills can be spammed, silence, stuns,binds they really are available again after 1gcd (stuns maybe 2). The knockback cant be spammed that much.

I liked your approach though, as to see that your last suggestion(smn dots under cover) worked out already, it gives me hope.
Well, as they don't want it to be overly complex adding more buff/debuff icons in the list to the existing cc effects would be a bit odd for them.