According to the lastest distribution, I see things like this:
- Bronze: Low level
- Silver: Below average
- Gold: Average
- Platinum: Above average
- Diamond: High level
- Master: Top tier players
- GM: Peak skill
- Top 500: Bragging rights
Silver-plat is what you talk about when you talk about the majority of players. Those three ranks house 80% of the playerbase. So yeah, if you are diamond, you are on the top of the pyramid. There are people above you, but you are already part of the elite.