I think you are completely correct when you say there is risk in not actually owning your mining hardware. But I also think that same principle of risk goes for everything else which you do not completely own. Just look at what happens when you leave your Bitcoin on the wrong exchange and they close up shop and never give you your Bitcoin back. Furthermore when it comes to mining, you are depending on the people who sold you the miners not to have included some kind of malware or spyware in the miners. And that the people who built the miners did not use defective chip parts and so on...