If I post something on Facebook and regret it, I have some control over it- sure, I can't delete it off Facebook's internal tape archives, but that's really going to be one of a handful of places it will stick around after I delete it.
If I embed something in plaintext on a blockchain it will be public, to everyone, forever. This seems like having less control, or at least no more control.
The case here is "yes", that's a certain type of control: the ability to put something up and never take it down. Kind of permissions on a disk where you can only write subsequent files but no one (including you) can delete old files. That is more control compared to someone who can write files but an admin can delete them.
Edit: my point is that it is control-less environment. So it is not answer to "where users do not have control of their data" problem.
If the GDPR (which regulates stuff around controlling who can even hold and retain data) is generally considered an attempt to enhance personal control over data, it seems to be using a totally different definition of control than one where it means "it's irreversibly public forever." A lot of blockchain projects seem to sell "control over data" when they mean the latter but allow people to believe it's the former.