interesting choice to be different than all other webpages and user experience for no good reason.

It is a non-optimal choice, but I believe there is a very strong reason. Not competing with the browser's native functionality.

Some of the most horrible web experiences, occur because websites try to take control of native functions. For example "smooth" scrolling, or highjacking the back button, or trying to abuse the clipboard! Confusing the user, breaking navigation, making the page less accessible and in some cases breaking after X months when browser or OS behavior changes.

What I have now is unfortunately far from "good" and there is improvement and experimentation waiting to happen, but the straight forward approach is not much better either...

What would you be competing with? Cmd/Ctrl-C/X/V for cut copy and paste are the norm. By allowing your app to use those keys you aren't overriding the browser, you're making your app conform to the standards. Even native apps do this. The OS may provide cut/copy/paste in an OS level text widget but it doesn't provide it in Word, Excel, Photoshop, or Audacity. That's up to the app. In the same way doing the same thing is up to the web app for anything not plain text.

Most web major apps do this. Office365, Google Docs/Sheets/Slides. Even Facebook/Slack/Gmail since they re-interpret the text (converting :-) into emoji and or replace with images.

Fair enough :) for cut/paste/copy it might definitely be a good option. Though what about control + S, should that prompt the export audio, or let the browser download the page?

Perhaps I should add support for the control key, but let other combinations were conflicts might arise. Getting good UX is a such fascinating topic.