The two scenarios are EXACTLY THE SAME.
In terms of purchasing power of the money holder, yes.
In term of inflation (the unit of value for calculations and contracts), no.
In terms of interest rates, no.
The economic decision making is different.
I think they are correct that the two scenarios are effectively equal.
With inflation, the purchasing power of all money holders decreases.
With demurrage, the purchasing power of all money holders decreases.
Total money supply = 2X, purchasing power = X vs. total money supply = X, purchasing power = X/2.
They are mathematically equivalent. In both cases the winners are miners, the losers are savers.