That's pretty much the whole point of the data ownership concept in the EU, though - force these companies to tell you exactly what they're using, and exactly how they're using it.

I don't really think there's a feasible alternative. Most people don't have the means, time, or knowledge to self-host all of the tools they use, and as a consumer, I can't really tell how a company is going to use the data I give them. In cases like that, the only solution is regulatory structure.