I'll say this. DRKs shouldn't have to be afraid to use their invuln skill in other content besides Savage (where it would be useful). Like some others have said, it is highly unlikely that you will get the full duration off due to it mostly being used for TBs or cheesing mechanics. They are very far inbetween.

The only time I could ever think of LD's duration being useful is Titania EX's tether mechanic where a DRK can eat all of the blasts.

It's just too risky and in most content, the DRK will likely die be it a new healer or a lack of time to recover from it.

And also, healers complaining about healing goes far more than having to stop to cleanse LD so don't pick and choose what healers shouldn't be angry about. Having to pause everything to heal through LD is quite annoying as even WAR and GNB only need 1 oGCD to actually survive whereas LD requires either Benediction, Synastry + Essential Dignity and possibly a Benefic 2, or whatever oGCDs SCH has available.

Point being that LD is not only annoying but it ends up more healer resources that could be used toward other things.

If they wanted a simple fix, then increase the incoming healing by 50% or lower the required HP recovered.