The item is now, essentially, a much worse version of 
- they both give the same AD and cost the same. 10% armor pen is not nearly as good as an anti-healing passive. Removing giant slayer mandated at least some sort of compensation.
I still don't see why they removed Giant Slayer.
Yeah it helped shred tanks even more.
But, like, nobody was building Last Whisper anyway...
The anti healing passive isn't always relevant. Some team comps don't have healing besides 
which is a high cooldown spell that only affects two people. You can expect LDR to amplify your damage by at least 4% more than MR in most scenarios.
