Giant Slayer and LDR too stronk?

Most ADCs have about what...? 1800-2000 health? So anyone with over 2500hp (which isn't a lot for tanks) will undeservedly feel the maximum effect of the item... Some targets that have around 2500 hp are pretty squishy... for example an Akali at level 18 with Rylais Crystal Scepter, will get destroyed by the Giant Slayer even though Akali is far from being considered a giant. The most tanky adc I believe is Graves, and he only has like 1979 hp at level 18.... Giant Slayer is supposed to be a tank destroyer.... So what's the point of the Giant Slayer if the 5k hp tank will take just as much bonus damage as the 2500 hp mid laner....