I disagree in parts. In e.g. an app on Ethereum you own your and the app's data more than e.g. you do on Facebook. It's because there are no gatekeepers that'd stop you from creating an interoperable app using the original data or straight up downloading the data. There's sufficient historical precedence of FAANG platform risk.
But then also "just owning the right to writes" may sell the concept cheap considering that in the realm of "owning data," there isn't many concepts besides "reading", "writing" and "accessing". "Owning the write" may be as good as it gets?
We tend to look at data from a materialistic view and represent it in our heads as .zip files or csvs. But data really isn't that. Data is continuous and owning "the right to write" is pretty cool IMO.