I cannot agree.
The punishment shouldn't be any different depening on the rank.
However, I believe that the punishment in general should be harder to avoid - it could be even lighter, but if you know you are gonna get punished - you are gonna think twice. Also, it should be aimed better - right now there are few types of punishment (chat restriction, ranked restriction, ban), but they are not aimed at the correct groups. For example right now ranked restriction is just an upgraded version of chat restriction aimed only on flamers. On the other hand, the leavers have only one possible punishment, which is timed/permament ban (even though giving leavers the ranked restriction would make sense).
I think the punishment should be more common, although with varying levels of severity... For example:
Leaving/Intentionally Feeding/Assisting Enemy Team:
Level 1: Warning
Level 2: Ranked restriction for 3 games (but without the chat restriction - this applies to all ranked restriction)
Level 3: Ranked restriction for 20 games
Level 4: 3 days ban + Ranked restriction for 30 games
Level 5: 14 days ban + Ranked restriction for 50 games
Level 6: Ranked restriction till the end of the season
Level 7: Permament ban
Offensive Language/Verbal Abuse:
Level 1: Warning
Level 2: Weak chat restriction for 5 games (you can still talk to all, but your messages are a bit limited (let's say 5 messages, but new ones recover twice as fast as normal chat restriction))
Level 3: Chat restriction for 30+ games
Level 4: 3 days ban + Ranked restriction for 15 games, and chat restriction for 30+
Level 5: 14 days ban + Ranked restriction for 30 games and chat restriction for 45+
Level 6: Permament ban
Negative attitude:
Level 1: Warning
Level 2: Inability to call a surrender vote and you automatically vote no on them + Weak chat restriction for 5 games
Level 3+: just as in Offensive Language/Verbal Abuse
Now, the** important part **would be - getting level 2 punishment shouldn't be hard. Like... Leaving two games in a row should immidiately give you Level 2 punishment, and so would leaving 3 games out of the last 30. Mind you that punishment for level 2 is usually rather low, so it doesn't hit hard - but it sure as hell should hit often.
Obviously, if someone both leaves and flames then he gets both punishments at once.
Also, in this case - the rewards for good behaviour (like the baron icon or the mystery gift) should still be applied to summoners with a single level 2 punishment (if you got multiple or higher level one then they shouldn't be rewarded at all).