Step 3 is valid if you have a cache plugin installed, if not just skip it.
Step 4 is mostly about the CloudFlare, but for Jetpack you need to contact their support to proceed with disabling the CDN temporarily for testing reasons.
For the Step 5, just deactivate all plugins event the ones that are bundled with our theme and check the case.
If you still have the problem of the Pro Editor being slow kindly get back to us with the URL/User/Pass of your WordPress dashboard using the Secure Note functionality of the post to follow up the case.
Also, give us the name of the page to test. Thank you.