While Cloudhashing didn't add hashrate to the bitcoin network others did so now cloudhashing competes more wit the rest of the network.
Yes, but that just means the time between blocks should increase. As long as I own the same percentage of the pool, the size of each payment should essentially be the same.
What? No!
You do not seem to understand that whatever hashrate you may be using is ALWAYS competing with the TOTAL hashrate on the whole network.
You against
all other hashrates, including others on cloudhashing.
Blocks are found at an overall
constant rate.
Since the ammount you got from your contract at cloudhashing stays the same while the rest of the world is increasing at a high speed, the portion you get will become smaller. To earn the same you would need more hashrate to compensate for the fact that others have more hashrate too.
You should read more about the mining reward system in bitcoin.