I'm still trying to wrap my head around all the economics involved. I think in this case, I'm tempted to go against my typical disposition against concentrations of wealth and power. A couple reasons why It bothers me a bit less in the case of Steem Power and interest, than it does in something like voting power, where I've been vocal in my criticisms of the imbalances.

First, Steem Power doesn't really exist. It's just an abstraction. The amount of VESTs that are represented by the Steem Power figure stays constant aside from increases due to participation and interaction with the community. The difference is subtle, but it basically means that the growth doesn't resemble compound interest so much as inflation. In Malthusian terms, it's "arithmetical" growth, not "geometrical" growth.

Second, we are still well above 90% vested, which means that powered up Steem is still experiencing quite significant dilution. This is something that I need to think through a lot more, but it does mean that SP is not earning the full value of its interest, due to the money supply increasing at a faster rate.

Of course, this might worry some because it does imply that Steem is overpriced at the moment. In the future there will be far more liquid Steem, which means that supply and demand will drive the price down. This might not be something any of us particularly want, but it's not due to the interest rate being too high. It has more to do with so little of the money supply being available on the market. It's manufactured scarcity.

I'm interested in seeing what kind of effects SBD will have on this. The whitepaper says that SBD will act as leverage for STEEM, increasing both the gains and losses of value that STEEM holders see from market fluctuations. I think it might actually provide some stability during sell offs. If the price of STEEM falls below a certain amount, there would be less STEEM in existence than would need to be produced if holders of SBD tried to redeem them. It could result in catastrophic failure, where both tokens lose all value... but short of the economics breaking down completely, I think it might provide price support. I've called it a "semi-automatic stabilizer." I could be way off base there, though.

Another reason why the interest rate doesn't bother me quite that much is that high value accounts which are not actively contributing the the community through posting and interacting will lose ground to smaller accounts which are more active. Over time, such accounts will lose their relative status... I wish it occurred faster, but then again of course I do. ;)