Having a pool of pre-erased blocks helps absorb spikes in write activity, but it doesn't let you escape the fact that, on average, an SSD will need to perform a

Having a pool of pre-erased blocks helps absorb spikes in write activity, but it doesn't let you escape the fact that, on average, an SSD will need to perform an erase operation every 128th page write (assuming 128 pages per block). If the device is kept at or near full utilization, eventually a fast operation (read) will get delayed behind a slower operation and your tail latencies will suffer.