This is being actively worked on, and performance has already improved significantly. More work being done, expect continued improvements.Daddy Dave commented
I really like OneNote and am trying to migrate my new employer into using it for R&D projects. It works well on Android devices but is toooooo dddaaammmm slow for online use. Why? Actually, it works OK once I navigate to the page that I want to edit, but that can take 30+ seconds to get there. Sheesh. Wouldn't you think that Microsoft would have learned how to create efficient web interfaces by now?