I've been using the new Outlook for a few months. I can't say that I prefer it to the old Outlook, but it does offer some advantages such as Archie within your email. Also you can create a task directly from an email which is handy.
When I first switched over to new Outlook, for a hot minute, I switched right back, probably for the same reasons you did. I then experienced the similar problem when creating an email from within smoke ball, it would pull up the new Outlook template for emails. It took a little while to load, required me to click a pencil in the top right of the email, when the pencil was very small and hard to see, and creates duplicate emails so that I can't tell if I've sent the email or if the duplicate can be deleted safely.
But initially right after I switched back I didn't want that new email template and my recollection is that I was able to fix it by going into the default extensions and change it from new outlook to old Outlook. Default extensions is a system setting that you can access through Windows start button