Yes, there are risks to running software from Microsoft (or any other vendor), Microsoft may not have my best interests in mind. However their software meets my needs and I have made the calculation that the value the software provides outweighs the risks.
I think what you're missing is that your calculation is rapidly becoming inaccurate. In the past, Microsoft had to make sure that their software met your (the customer's) needs or they would lose that customer. Their best interest was to prioritize the best interests of their customer base, because they would then keep buying Windows-based computers which is where the revenue came from. Now that the market has shifted, they are placing their interests before that of the customer, and the value of the OS is thus diminished. What people are talking about is not the status quo you refer to that has been true for a few decades, rather it's the status quo that seems to be coming which looks much different. It's one in which you are not the customer to which the software needs to provide value, you are the product. The software will be providing value to the actual customers of Microsoft, which are likely those who want to advertise to you, sell to you and monitor you.