If you do manual focusing with the lens, the Image Stabilization is very important. STM lenses are only good if you are depending on the cameras built in phase detection autofocus. In other words, you want the lens to do the focusing for you.
1. STM is for people who want the lens to focus for you through live view when recording video.
2. IS (no STM) these lenses are used to manually focus in video...but the IS helps keep the video from being shaky while you are hand holding the camera.
Right, my point exactly. If I have to do all the focus manually, I don't consider it's good for video
You don't know what you can do when you don't know what you can't do.