"there isn’t much point to building the item anymore". Calm down, the skill is still pretty effing strong.

I think most can agree that the following attributes are what make the skill "OP":

1. Magic Immunity (Illusion cannot be instagibbed by hex, dagon, mana/health drain)
2. Cooldown (35s cooldown means the skill is spammable, and you pretty much have it ready/are able to use it in every teamfight)
3. Outgoing Damage (150%, self-explanatory)

All 3 attributes were untouched.

The nerfs.

Illusion's incoming damage increased to 350%: So, similar to Manta illusions now. I'm sure you have been in a game where you see an enemy Naga send his Manta illusions to split push. Impulsive you thought it would be a good idea to stop the push by killing the illusions. 3 nukes and a couple of right clicks later, illusions still have 1/2 HP. You regret everything.

Grim's illusion is pretty much that, except you can't nuke, stun or slow that thing. Oh, it also punches harder than prime Mike Tyson btw. :D

Scepter illusion duration reduced from 20 to 15: Honestly, this nerf is whatever. 15 seconds is still sufficient time for the illusion to wreck havoc in a fight/bully lone enemy supports.