I am in almost exactly the same boat. I built my first Wordpress-based website in 2005, and it is still online today. I've had to employ a constellation of plugins (some third-party, some home-grown) to keep Gutenberg from mangling my content. Gutenberg could have (and in my opinion, should have) been just another official plugin. Instead it's trying to break my site's bones so they will re-heal in a new configuration. Begone unwelcome meddler!