We’ve updated our plot of return on stake (ROS) vs pool size for epoch 215. The ROS is calculated based on pool performance from epochs 213 and 214.
Notice how the pools with very high ROS have not minted very many blocks. Luck plays a large factor in ROS over a short period and will even out over time. Given the same performance, actual annual ROS will be about the same regardless of pool size, as long as the pool is not saturated. (See our recent post showing a breakdown of staking rewards here.)