That is very innacurate...1/3 +1 only gives the "attacker" ...

https://steempeak.com/steemtron/@lauch3d/there-is-no-51-attack-in-steem

Good thing we can agree on reducing the number of witness candidates a vote can be cast on. Most importantly, should be 1SP = 1 vote. One can vote on 5 candidates, but each would get only 0.2SP worth of votes.
30 is too many, no average person can make an educated decision about so many candidates. See my post for the details.