I would argue that under both proof of stake and mining your income is always directly proportional to the amount invested, either in equipment or stake.
The main difference is the minimum barrier to entry, however under PoS you have access to various pooling services, which simulate consumer scale mining (complete with the associated inefficiency).
The main difference is the minimum barrier to entry, however under PoS you have access to various pooling services, which simulate consumer scale mining (complete with the associated inefficiency).