If a whale disagrees with a post and it's payout all he needs to do to affect the rewards pool distribution is instead of using the full weight of his it negatively, to use it positively and upvote a post the believes has virtue.

Your premise is dead wrong. While that will give someone a better potential rewards, it does nothing to solve the problem of the over valued post other than possibly lowering it a small amount. A very small amount.

So instead of simply denying someone their earnt rewards he can upvote someones post significantly.

Well, there is where you have yet another fallacy. The rewards are not earned until the end of the seven day voting period. Until then, they are potential rewards and subject to movement up or down. That movement can be shifting in the reward pool due changing STEEM value or voting patterns or it can either up or downvoting.

The system has to have balance and that means the ability to both increase and decrease potential rewards.

The system will not be changed from that basic principle so I guess you're going to either need to adapt or decide this platform isn't for you. It wont be for everyone.