True enough, a vote-only bot can't be flagged down. But they also can't be flagged up and boost their reputation above 25, so such a bot is a mosquito, like the one time famous @ asshole bot. That was run by nextgencrypto aka berniesanders. I left out their @ symbols because I don't need that cunt weighing in here.
Furthermore, if the botfarmer paid for the account, that's another $5 worth of market cap, or if they use the 'freemium' free account type that will be added in Calibrae, the bot will be heavily restricted, unable to have Stake delegated, and besides that, with starting rep score, its actual influence level will be even smaller than a 25 rep new bot account on Steem.
The power limiter effect of reputation is calculated by the highest reputation account in Calibrae, which sets the 100% coefficient level. Probably that will be around what is 70 now, which is about 40 billion rep points. This would put the coefficient of a non-upvoted account at around 1% or even less, so loading it up with a million bux worth of Stake would only make it equal to a $10,000 account on Steem. If they want to put that much into the market cap, and by this only gain that much power, well, that's still good for the platform, and the effect of their votes will still be no more than a 20k account at 50% of the top reputation level.
By making reputation a coefficient limiter on vote power, this kind of abuse is made very expensive. The moment the bot makes a squeak, also, the users can pile on high rep downvotes and once it drops under zero, I am thinking the logical limit drops to 1 post a day, or vote, and that's gonna burn the botfarmer-troll...
This sounds like an amazing idea to not only fix the bot problem, but also to make reputation much more meaningful while limiting bandwidth for those that don't deserve it.
On the other hand, it seems that you're saying those with high reps and high stakes will essentially be gods on the platform, with even more say with what goes on than on here. There must be enough at the top to keep others in check, and I haven't the slightest clue what number/percentage is ideal, but if the top weight/rep is concentrated in few hands, the probabilities of an oligarchy forming are quite high IMO.