Do you mean 4% in USD terms or Steem terms? Someone calculated that in a comment to my post Steemit Reward Pool Abuse, Myth or Fact? He found it amounted to 25% annual ROI in Steem terms. That is still a good deal of money, if Steem manages not to lose its value against USD.

4% daily would be an insane ROI especially if you consider the near 0% interest rates nowadays. I can only imagine that happening in USD terms when Steem is making a rally. Otherwise, it doesn't seem possible or sustainable to me.

By the way, as I said above, the ROI is the same for accounts of all sizes. Smaller accounts are especially advantageous, because no one cares about them.