I am not sure what kind of research you are talking about. Most of the times, cloud mining is not profitable than buying and holding.

Say for example btc,
1 Btc was 1k at the beginning of 2017. With 1.5k investment, you would get 1.5 btc. If you have invested in cloudmining, you would have earned 12.5 T hash power which would have generated .33bTC(Website shows .45 btc) due to the mining difficulty.

At the end of 2017, BTC was $13,200. So through hashflare, you would have earned 13,200* .33btc = $4,300
Whereas, if you would have bought btc and sold it on Dec 2017, u would have got 13,200 *1.5BTC = $19,800.

Increasing difficulty level is a major concern in Cloud mining. If you look at the Hashflare site, their calculation wont include increasing mining diffulty. BTC, eth and monero difficulty increased 490%, 468% & 1500% respectively. Hence, less coins will be mined than mentioned in the cloud mining website.

Cloud mining websites and CryptoCompare wont have the difficulty increase in consideration as noone knows how much the difficulty is going to increase in future.