I think the biggest problem is that the number of votes that one account can give (30) is bigger than 20 the number of top witnesses.
In order to solve that we should reduce the number of votes so from 30 to 10 or 5 or 1 and in the same time increase the number of the top witness from 20 to 30 or 50 or 100...
in such a way as to increase the decentralization of decisions or democracy (call it as you want)
But if this will not fix the issue, so maybe we could also adopt some non linear curve that decide the power of the vote. For example a Gaussian function where who have more than a certain value of SP and who have less than a certain value of SP have less power.
In this way who have tons of SP have the "same" power of "normal people" and in same time it can disadvantage the creation of million of fake accounts with malicious intent.
This is just an idea, i know this problem doesn't have a simple solution, but with the time we can improve the system.
Nothing is perfect in the universe
Bye bye