There are probably 1000 markdown editors out there ranging from a simple textarea that only lets you write text, to Emacs, and something like Msword on steroids. The nice thing about an open market is that when you no longer like a product you can just switch to another one.

I however understand your issue with privacy as any app can just steal your content without you knowing. The solution for privacy is to sandbox/jail the app into an environment where it can just access a limited set of resources, for example you can use an apparmor profile where the app can just access a special folder, and disable all networking. That special folder could be your google drive mount.