Windows 7 is still dramatically less secure by design (i.e. not missing patches but architectural changes) compared to Windows 10, even Windows 8 had some meaningful kernel security features that 7 lacks. This includes sandboxing measures that Chrome & Firefox use, meaning you're still less secure even if you're not downloading shady software.

You're frankly better off applying a bunch of registry changes to 10, using a Education or N (EU) edition "illegally", or blocking DNS than going back to 7 just for privacy concerns. You're cutting off your nose to spite your face.