First of all, technically, integer is preferred (1, 2 or 3 for instance). Secondly, Sybil issue is not relevant because there is no difference between one big vote from an account or aggregated small votes from multiple accounts.
As @sigmajin well pointed out, the basic assumption of n^2 is equally distributed stakes, however this is not the case in the current Steem.
The only issue with linear system is self-voting. Regarding this, please see my comment above. IMO, self-voting is not a serious issue in the linear system.