This is a good point. I'm using a few google apps in a single profile and was using Gboard until a few moments ago. Just found Heliboard on F-Droid. It's based on the AOSP Keyboard, it's configurable in a gboard similar fashion, doesn't use any network permission, and, if you miss gesture typing, it gives you the option to load the library from a folder, which I did.
Obviously it's the proprietary gesture typing library from Google. You can also get it from any gapps package. Else, their github has a link to a github repository where it's available.
I can't tell if the library itself can share data via mutual consent to any other google apps. But at least you have the option to load it or not hence, solving the problem op hilighted.