Mining is over 3 times less efficient. Unless that ratio starts to change, miners will drop off to the point that the coin is in danger due to low hash rate.
The impression is of the rich just getting richer and the little laborers getting sweatshop pay, and it's a huge turn off.
1. Are you using the latest amd / nvidia miners? They have better hashrates.
2. If hashpower is significantly reduced, block reward goes up to compensate miners. Instead of 5 DRK per block it could go to 6-7-8-9 etc.
3. You must also calculate the compound effect of mined DRKs that can be used for masternode mining, something that alters the profitability calculation compared to other coins. If one makes 100 DRKs per month and he can use them to buy a 100 DRK slice of a masternode, then these too generate profit in subsequent revenue streams. Hence the miner's reward is not mutually exclusive to the masternode owner reward, rather they are complimentary - supposing that the miner holds and uses them for MNs. After you factor that in, a different picture emerges.