I think that's the aim, not the failure of this plan.
The key difference is that instead of companies storing, owning and exploiting your data, the user maintains their own data store and companies can then access and exploit it.
It's decentralised in the way where the data lives and is controlled by, not in how or where the data is used.
There is the problem where companies could continue to use your data when you no longer let them access to your data store - but that in effect is at worse unethical and at best not legal these days.
The key difference is that instead of companies storing, owning and exploiting your data, the user maintains their own data store and companies can then access and exploit it.
It's decentralised in the way where the data lives and is controlled by, not in how or where the data is used.
There is the problem where companies could continue to use your data when you no longer let them access to your data store - but that in effect is at worse unethical and at best not legal these days.