The v5 templates and emails are imported as html, that's why you see the default editor.
When creatinmg a new template Acymailing offers you to choose to create a html template with the default editor or a new template with the new drag & drop editor. When creating a new email the drag & drop editor is used by default. If you would like to continue with html you should start from a html template,.
We fully focus on the drag & drop editor. That's why we suggest to recreate your templates in the new drag & drop editor.
As for the Joomla articles, I guess you refer to smart newsletters. These are in v7 referred to as automatic campaigns and you need to recreate those. V7 is using complete different techniques compared to v5. Because of the huge difference smart newsletters cannot be converted and have to be recreated.
Please raise a support ticket to get assistance with the old newsletters that are not migrated. You can op a support ticket here: https://www.acymailing.com/support/