Did he not pay for the Steem Power that he purchased?

I have no idea the terms of any deal which may have happened between Justin, Ned, and Steemit. The rumor is that Justin bought Steemit, the company, and not the stake directly, so I fail to see how a change in the shareholder list would make any difference. The company is not the blockchain and the blockchain is not the company.

Apart from that, as many others have said, a change of ownership even of the stake doesn't change anything. Could Justin sell everything back to Ned, and Ned would then be off the hook for any statements that he ever made pre-sale ("That was Old Ned, I'm New Ned, please don't try to hold me accountable for anything that Old Ned said"). This is absurd in my view.

And regarding the "consensus-breaking block" its irrelevant... are you trying to say that people can buy Steem but not too much so that the witnesses keep their control? Bad message

That is hypothetial. It is much more difficult to buy a controlling stake on the open market. That is one of the premises behind any proof-of-stake system: that buying up enough stake to break consensus is extremely expensive and unlikely. If that turns out to be false we will have to face the fact that proof-of-stake (including DPoS) is a lot weaker than we thought and may not be able to be trusted. But again, that is hypothetical. Buying up a huge block of ninja-mined/premined/etc. stake that was described as non-voting is not hypothetical.

aren't all the witnesses aware of many "ninja-mined" stakes that are out there?

I'm not aware of anyone other than Steemit who manipulated the mining to guarantee the outcome they wanted (effectively an 80% premine) by withholding information, posting broken mining instructions, resetting the chain when it didn't go their way, making public statements about how the ninja-mined stake was not going to vote on witnesses and earmarked to develop the ecosystem, etc. No one else did that. Steemit did. The situation is unique, and you can't wash away that history by selling a company.

Also, I'm not a witness, just a stakeholder like you, and I am voting to support the witnesses who are running the update. Your logic in trying to convince me to change my mind is seriously wanting, but you are free to vote your way and the votes will decide it. I'm not even sure what is the point of all this noise when we have voting. Don't like what the witnesses are doing? Vote them out!