While I do agree it looks unfair, the "rich" also risked the most, so it's only fair they get the most. Bigger risk = bigger reward. Bigger risk also = bigger loss.
With an equal percentage per annum (4.5%), the rich coin holder gets more coins due to the amount of his contribution. The contribution of 5,000 coins will reward 225 coins for the year. While the small holder of 100 coins will get only 4.5 coins per year.
225 coins is the reward for higher risk.
Your model is unfair. And most importantly, it will lead to the centralization of coins in the hands of large holders - because they get rich ahead of ten times faster than others.