The higher a pool's hashrate the less your variance is (unless the pool is PPS in which case the pool size makes no difference.) A small pool variance over the short to medium term means you could end up with far less reward, but conversely you could also end up with far more reward. Pool hashrate does not affect your expected earnings. The only difference between pools in expected reward over a long period is the pool fee and whether the pool pays out transaction fees to miners or not.
Incorrect.
A very small pool will effectively reward your work at a much later date due to finding blocks rarely.
The result is that your rewards can be based on a much later bitcoin difficulty, and thus expected to be rewarded much less.
If a pool doesn't find at least a few blocks each difficulty change, i.e. each fortnight, then this will be much more apparent.
For example, the last difficulty change was a bit over 13.5%
Any shares mined during the previous difficulty, but paid in this difficult change, will have an expected reward of 13.5% less!
If those shares are still unpaid for this current difficulty change, then it of course continues to get even worse next difficulty change.
For example, shares mined 2 difficulty changes ago 4.4% + 13.5% compounds to a 18.5% expected loss over those 2 difficulty changes, if the shares are rewarded now.
The longer this goes on, the worse the expected reward becomes.
For example, shares mined during the difficulty change that ended on the 10th of May, if they were rewarded today, that would be a compound 54% less expected reward for those shares - i.e. less than half the expected reward.
