Let me propose a counter to the question in play. Let's engage in a thought experiment.
What if @blocktrades and @pumpkin were controlled by the same person or people? After all, as we can observe they don't have any overlapping witness votes so in principle may very well could be animated by the same intent. As such, we can go a step further and assume that for both of them, their voting behavior is orchestrated by software and not manual human intervention. Building bots to do that sort of thing is right next door to trivial.
How would the animating power be lessened by splitting the steak across multiple user IDs? As far as I can tell, it wouldn't. Given that the voting is managed by bots anyway, it doesn't matter how many accounts that SP could or would be spread across, the only important consideration is the sum total of SP/mega-vests controlled.
Would a whale be willing to do that? We've certainly seen evidence in the past that very large stakes have been split across coordinated networks of accounts in order to try and conceal the actual voting volume involved, so we know for a certainty that a whale would be willing to do that.
As such, reducing the number of witness votes is pretty clearly not an impediment at all to individual or group stakeholders who want to control the witness hierarchy. After all, the underlying architecture of the blockchain is intentionally designed to give that power to those who hold the stake.
I think it's safe to say that if the pool of active SP is currently decisive, it wouldn't matter how far it was split, as long as the voting is coordinated that decisive power remains.
Coordination is easy and cheap.
I agree with what you say with some distinctions.
By spreading the stake across multiple accounts and voting for the same witnesses, whales have accomplished nothing in terms of influence. It's the same. They may conceal this way the fact it's coming from the same account though.
If they do it to vote for different witnesses, then the influence spreads thin, and they can be overthrown by smaller votes acting together.
If consensus remains of 21 and number of votes per account diminishes to 5 or 10, one account cannot 'control' as many witnesses, unless I'm missing something. It may be a good measure.
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