That seems like a very noobish argument, in my opinion.
I read the jutsu and it says that when the person attempts to preform handseals or concentrate, he/she gets a spasm of pain that blocks their concetration and thus their jutsu. And your jutsu requires you to expell Lightning Chakra so powerfull that it reaches Forbidden Rank and then shape them into shards, and then controll them into covering 360 degrees of your opponent. That's more then in the description of the gen.
Sharingans allow you to see through a gen, and know when you are or not. But it doesn't say that you don't get the same effects as if you haven't the Sharingan. The fact is that by knowing something is a genjutsu, Sharinga users were able to ignore it, and thus act like it doesn't affects. In this case, even though you now you're under a genjutsu, as you try to concentrate you feel the sudden spasm. Not much for the pain, but for this sudden effect. And it's your body that feels it, not your sight.
The fact that it is a D-Rank doesn't necessarily means it's weak. It can also means it's simple or easy to do. In this case it isn't weak, it's just pretty basic. You aren't immune to it. If it was based on putting you into an extended period of pain, your rank and endurance would make you immune to it, in little time. But this sudden effect is what makes the jutsu brilliant.
And the no handseals thing, I think you're wrong, and a second Mod/Sensei should check it and then add it in the KG Restrictions jutsu.
Nothing further to add, so I'd like to conclude my post saying Kiwii's move is valid and it's now you're turn to counter it.