You are correct that Stream does not have all the features of Office Mix and as such you don't have a way to continue doing what you were doing. Sorry.
Watching videos without O365 Login
This is on our roadmap for Stream. We are looking into both pubic anonymous video playback and named guest users. No timelines I can promise at this time but this is higher on our list.
We have done some high level discussions with the PowerPoint and Microsoft Forms teams. We think that eventually something closer to what Mix could do would come by the combination of our 3 teams. However these are just early discussions and we don't have a clear roadmap here yet.
This works today in PowerPoint if you use the "Publish to Stream" button that recently was added. We allow you to attach your PPT file to the video as it's uploaded to Stream. But this doesn't get you what you want in terms of survey/interactivity, etc. It's just a way to keep the original PPT around with the Stream video for future download and edit.