% ROI usually come with a time-frame.

What you meant to say is that you give back a % of the profits (90% of 75% and keeping the curation reward).

Disclaimer:

Since the money come from Steem inflation of ~9%/year and that some of that inflation puts a downward pressure on the value of STEEM it's a risk-free way of earning more STEEM but it is not a risk-free way of increasing your USD or BTC purchasing power.