Okay, I really do not use Sidecar much but will say that this week it has been a life saver. I have a presentation to give at a virtual meeting the must be submitted in a week (why virtual meetings must far more stressful than face-to-face meetings is a mystery to me), but life got in the way (i.e. Covid) and I am scrambling to get a rather large dataset analyzed to meet the deadline. I dawned on me that I could use my Apple Pencil with Sidecar while using my iPad as a second screen. My analysis requires me to trace a whole bunch of infrared images in a software app called ImageJ and doing this with a mouse is painful. So, in comes Sidecare. The ability to do this with my Apple Pencil instead has cut the time for my workflow in half. Actually did all the analysis in about 2.5 days which is amazing! This might not mean much to many of you but it was a freaking awesome to me.
I am awaiting the day when I can use my iPad to draw on/over or control drawing in some of my core macOS apps with far less no friction. Knowing how ImageJ works, I see your use case as a perfect example of the savings afforded to exactly these kinds of work flows.