Only if they had enough stake, but it would require MORE stake for them to control the entire top 20 witnesses by limiting the votes per account to 5 than it does currently.

For example, an 8 million steem account splitting stake into 4 accounts now only gives them 2 million per account to vote with, a number that is much easier to match by other voters on other candidates, than matching the current 8 million total, like there is now.

Overall I am not doubting or claiming that the largest stake holders should not have significant influence, but when we have 2 of the largest stake holders basically deciding all of the top 20 witnesses (who are in charge of dictating the direction of the entire steem ecosystem) we need to adjust the model.