For example, If I were a business that would want to use the Ethereum Blockchain technology to shift my business to Blockchain, wouldn't Ethereum be in control of the actual underlying Blockchain technology? Wouldn't it have the power to for example change the consensus algorithm or change the underlying technology? If I am missing something here please explain.
That is true if the business is running on the main public Ethereum blockchain. Besides that, you would control the business. However, the application would not be running on a central server or a cluster owned by a single entity. The application would be installed and running in a decentralized environment, i.e. the Ethereum main chain.
On the other hand, many businesses might have their own "private" blockchain. In that case, the level of decentralization depends on how it is set up. However, the Ethereum Foundation would not be controlling the underlying technology because the business would control what software client and version is being used. Since Ethereum is open source, a business could even make their own changes to customize the Ethereum client that it runs on.
For example, If I were a business that would want to use the Ethereum Blockchain technology to shift my business to Blockchain, wouldn't Ethereum be in control of the actual underlying Blockchain technology?
No. What determines the rules the blockchain follows is the software that the users of the blockchain run. Nobody has any special power to make anybody else run software in some particular way. They can only try to convince them to change.
For example, when the DAO was drained, proposals were made for ways to restore the stolen funds. Nobody had any authority to force people to make those changes, and so some people made them and some didn't. That is why you have both ETH and ETC today. Those who disagreed with the plans were not in any way compelled to accept the changes as nobody had the power to compel anyone.