Hello ShinShya,
I believe the Full Tilt rake is dealt - so not contributed rake (the same on which your rakeback is based). As such the table rake divided by the amount of players in the hands.
Earning around 150 SP a day is actually not that little considering that holding such volume would put you at Platinum (the second highest non-permanent PS rank). The reason the highest players have so many points is that they are playing either extreme high amounts of volume or just very high stakes - where the rake is proportionally high. Many are playing playing 5/10 to 100/200 FL (or NL1k+ / SNGs of 109$+) which can bring them anywhere from 1,000 to 8,000+ StrategyPoints a day.
As you are still playing NL50 and the surrounding limits - I wouldn't pay to much heed to competing with them yet though. As long as you are Gold-Platinum you have access to the most important educational content - as well as the Hand Evaluation boards (which I would highly advise getting involved in: Hand posting guide)
If you concentrate on improving your game through articles, coachings and videos the points follow suit, as you move up in limits.
Your goal should be to improve further and further - so be sure to not spend too much time grinding - but also planning in time for studying and evaluating your game.
Most of the people dominating those leaderboards were highly active in hand evaluation and discussion on their path to the high stakes
Best regards
SoyCD