Hey,
Most of JL bans handed out recently are 1 day. 3 days is a rarity. I'm not saying it's not just for the offenders, but currently filling a bug report is a lot of work. And processing it on your side is some work too. One week CL ban isn't very impressive either.
Why would I spend 15 minutes of my life to punish someone in a way he can hardly feel? I don't think bans that short serve as any deterrent, unless someone plays a lot. Most people have other games, play maybe one or two lobbies per day… So 1 day ban is hardly noticable for them. CL bans don't hurt them at all usually.
I know if griefing was fun for me, I wouldn't much care about bans that long. And as a legit player I feel like my time gets wasted twice: first time by the griefer, and then second time while filling the ban report. And all this for a one day ban?
I think longer bans would deter the offenders more and make people more likely to actually report players.