Mastery Points for Junglers seem a bit off.

Me and my brother have been sharing a computer and both of us have played junglers quite a few times since the new mastery system has been released. Since I figure some people will ask the champions we have used are: Zac, Nautilus, Jarvan IV, Rek'Sai, Skarner, and Nocturne. We've had both good and bad games with all of these characters but in none of them did we achieve an S rank, the highest being me getting an A+ on skarner for carrying (I had something like 2/0/15).

What I'm getting at here mostly is that I think the mastery system relies too much on kills and doesn't give proper value to assists. Most of the tank junglers don't need kills and would prefer to give them to laners. My brother recently had a game where he went 2/6/30 - he was there and participated in 32 kills out of the teams 35 but he only got a B. I am not here to complain but mostly to argue, I am wondering if anyone has the same concerns and if this is an issue elsewhere?

Another reason for me bringing this up is that I find getting A or S ranks as a laner is almost too easy. I almost always get it when I go positive in lane and I find that a little ridiculous that junglers seem to be gimped for helping out lanes but not getting kills. Any thoughts on the matter is greatly appreciated and would like to hear feedback from some of the community on this!