I believe that 20% is fair, the risk of cryptos is still very high compared to fixed income/equities and as the whitepaper was structured like this, we already had an idea of the inflation of the token, probably in the future it could be revised to 18%, however quickly changing the percentage would not be good for the token in my opinion
If there is some change it should be gradual in my opinion. However we jumped from 0% to 12% and then from 12% to 20%. I think it will be more difficult to get a general agreement to do it the other way around ;-)
The Whitepaper does not suggest that the interest rate shall be 20% :)
Quite on the contrary, the very original one says that it is content creation, curation and commenting what should be rewarded from the inflation. Instead, you take a share of those rewards for activity and appreciate inactivity - passive staking tokens to Savings.