The unfair advantage of n^2 is the same if the SP is in a person’s one or several accounts all voting for the same content.
True, but at least such a whale would have to spread his Steem power on many different accounts, so that every single account had less steem power - also the ones executing the last upvotes in the row. Apart from that he would have to own quite some accounts to profit from the n^2 effect ...
I still think either a sigmoid reward curve or a curve which starts as n^2 and ends linear are at least worth to think about ...