This is coming from a Kha'Zix Top Main, The removal of his damage reduction is a case similar to what happened to Akali's. The reasoning was that while it gave Kha something to fall back on if behind, it had the ability to allow him to push to lead even further since he could ignore damage to allow for his burst.
His utility is still amazing, even if it doesn't come till late game since W is now the third evolved ability.
I will agree his burst damage is gone, making him more viable as a bruiser, or closer to a full tank for his heavy utility, but his slows make him useful to a team even if behind.
The only thing I really wish they would do is reduce his isolation range if only a little bit.
TL;DR
Damage Reduction removed for a good reason, Kha still has utility, kinda useful if behind, smaller isolation range PLZ.