Hi there!
Yes, you are right! You can do everything in the frontend editor with the new SP Page Builder 4 version, it will give you live drag and drop editing interface. No backend editor anymore.
You may check this related blog post:
https://www.joomshaper.com/blog/joomshaper-plan-for-sp-page-builder-3-x-series
Downgrade fom SPPB 4 to 3 is not recommended and may leads to inconsistency. However, if you have regular full site backup, then you can go back to your last working backup when there was SPPB 3 version.
Best Regards