So now that I properly understand your design, I can more easily identify the flaws.
I think were are on the same page now, maybe with the exception of one very important aspect: Interests on coins are credited to every account every time a block is built (by anybody).
So, interest alone cannot be an incentive factor to buy more than one account since you get the very same interests (at the same pace), no matter how you split up your coins
between your accounts.
But those with more stake can afford to buy more mining accounts, even though they don't have to. And thus if denying others interest is relatively more profitable for them... ______________ (fill in the blank yourself)