Your title is a gross oversimplification of the problem and I don't believe it is an actual quote from Riot. If it is then you are leaving out additional information that would follow.
IP bans are very, very easy to circumvent. In most cases you can just unplug your modem and plug it back in.
There are two main reasons you would not be able to circumvebt them. First, you could have a personal static IP for things like hosting small servers for friends, like a minecraft server. These are rare as in most cases you will just set the server up when you want to play and you can give them the IP address then.
Second, you are using the network of a business or other organization. This is what you talk about in your title, and it could hit a lot of people that did not do anythi g. People would probably make accounts to get their college (collage? idk) banned for kicks.
Now for the posts in the body of your post.
The reason you see more smurfs than noobs is because you are a smurf. The game attempts to detect these fairly quickly and pair the like ones together.
The second issue is potentially a problem, but a lot of those accounts are detected and banned.
The third issue is true, but it is why new accounts are punished more quickly than higher level accounts.