Lord Dominik's Regards have the same issue old Last Whisper had: effective against non Tanks.
Riot finally changed LW to only penetrate bonus armor because everyone had enough base armor for it to be effective aynway.
Now I think LDR has a simmilar issue, because a lot of Mages and Supports build some health, "some" being already close or over that 500 cap on LDR.
LDR should scale to 1000 maybe even 1500 health difference. Because that's what most Tanks and some Fighters will get.
Edit, to clarifiy: I don't mean that LDR shouldn't have an effect against Mages and Supports that build tanky. i just think it shouldn't reach it's full effect in the range of one major health item

I usually get
+ scaling hp seals. That makes it 616 bonus hp at level 18. 727 if 21/9 masteries.
yeah, I'm pretty sure the fact that this item is almost 100% effective against just 1 health item is a pretty good example of that...
also, lol Grievous wounds.
passive on Lord Dominik's Regards, remove Blade of the Ruined King, and call it a day? Wouldn't that be better?
will literally tear through any Singed, Vlad, or Mundo player in one second, down from two.