Ah now I see where you are getting the ROI of 10% from. You are calculating the ROI in USD not in Steem.
But I don't see any reason to do that for this time though.
Buying votes from Smartsteem (or to be more precise rshares) is only possible in Steem and SBD. Right now with the 50/50 Payout in Steem and SP, it is quite easy to see the direct effect of a specific Steem investment and the (estimated) payout.
Today 20 Steem would yield 22.4 Steem, which is better than the advertised 10% ROI (in USD).
Shouldn't it be possible to calculate the possible payout in Steem with a given amount of rshares and to fix the ROI in Steem not in USD?
Even with a payout in part SBD, the internal market from Steemit would provide a direct price for SBD/Steem, without the hassle to go over USD.
What is the benefit of calculating a Steem Investment in USD and why are you doing that? Still kinda curious.