It's not just the data available by default, it's also the very advanced user interface allowing even somewhat non-technical people to produce their own reports and dashboards.
Yes, you only co-own the data together with Google, but at least you have the data compared to using a home-grown solution which will either not provide your product managers with what they need or which will consume all of your life as you slowly re-implement your own Google Analytics which will never be as good and/or featureful as the original.
Of course, if it's just about your personal blog and if you're willing to spend some time on the tooling itself, then yes, tools like these don't have the privacy issues otherwise accompanying third-party analytics.