Many services and companies argue that metadata is not personal data, but even if that were true by definition of the word, the means to correlate metadata to a real person have existed for how long now?
Just knowing that I receive messages, at certain times, in a certain app, might not be a lot on its own, but as soon as you cross-reference that with other users, it becomes a surveillance goldmine.
And that's what many people seem to miss, I think.
Individually, there might not actually be much, depending on how you use your device. But the word individually gets thrown out the window in our world where everything is interconnected 24/7.