mining pool hashrate does affect your earnings as the 25btc block still has to be split by how many shares you submitted so for example a block took 100 shares and 1 user submitted all those share they would get 25bitcoin where as if 2 users submitted share they would get 12.5 each
Indeed, but in the case of two users, you would win blocks twice as quickly since the pool's hash is doubled so the overall earnings would be the same.
so in that case blocks should be found faster and faster...
the way bitcoin work is the difficulty controls how fast blocks are found by the network and hashrate allows even distribution among the mining pool that finds that block that way if someones putting in 2ths and someones pitting in 1mhs there not getting an even share of the block so if the 2th miner increases to 6ths he will see his mining profit per block increase and the 1mhs miner will decrease