I've done some calculating and have come to a conclusion that everyone gets ~5% rakeback on PokerStars.
Also, I can't fathom how they justify their "everyone has unique rakeback". Here's an example: nl5 player needs 2250 points to open a silver chest and nl50 player needs 6000 points to open a silver chest (the players in question are me and my friend and we have cross-checked all the info). $1 rake = 100 points, so the nl5 player needs to rake $22.5 and nl50 player needs to rake $60 for the same chest! And it's not like they get different rewards, the rewards in the silver chest are the same for all! This is just insanely ridiculous. It is pure discrimination of players who player higher limits. Granted, nl50 players get random cash prizes in chests of $10 and at nl5 they get $1 usually, but that still doesn't make up for the huuuge gap as those cash drops are totally random.
Basically they have totally decimated the rakeback system. I know they are a private company and they can do whatever they want, but they can definitely no longer claim that they are the best in the business and that they have the best loyalty program.