Making alts aren't against the rules, as long as you aren't farming with them in official servers. Same goes with all the other rules like scamming, etc..

Also, it honestly could be possible that it is a combination of both alts, and new players.

There is also a great possibilty that people with higher ranks that play noobly are rage quiters. You've got to take into account all the possible reasons as to why a low belt has such a high rank.