Goal is to give you a payout of 50% SBD and 50% SP.

No, it's not. Goal is to give 75% SBD and 25% SP. That's the whole reason witnesses are adjusting their price feeds. To print more SBD.

So you get 5$ worth in SBD and 5$ worth in SP.

Nope. You get 75% of the entire value of your reward in SBD and the rest in SP. Please have a look at your own rewards to see how this plays out.