The downvote pool is not going to fix things like this. The best way to stop this type of behavior is to increase the legitimate demand for the service that the voting bots provide. That service is advertising.

The cost of that advertising is based on a market. There is a limited vote value among the bots, which is the supply, and the people buying the votes is the demand. Right now the demand is so low that buying votes is profitable - meaning that bots are effectively paying you to use them.

If the situation were reversed and there were more legitimate brands or businesses that wanted to promote their posts to trending, then buying votes would cost money - which is how it's supposed to be.

If that were the case, then only people who could actually get value out of promoting their posts (i.e. they have something actually valuable to promote) would pay for the service.

So tl;dr to fix the problem we need to get more legitimate demand for advertising on Steem-based sites.