The stock AOSP keyboard is certainly lacking. We have had plans to try and integrate a keyboard in the past - but it's fallen short due to open source licensing issues. Sorry...!
There really wouldn't be an issue with using a Keyboard app you trust. Some people use an app like yours, Helium OpenBoard and FlorisBoard (Alpha versions *only*). Some may use GBoard or another keyboard app and disable the internet access as well.
It would be nice to have an improved keyboard and it's still considered.