(post update)
The everything on one page for course editing is more confusing than the tabs were to be honest and it makes things LESS organized since your eyes get lost on the page. I understand why some people might want that though for ease but with the old tabs up top it was easier to understand what section you were working under and muscle memory could get you there much faster (since now every page has different formatting since the format is adjusted to fit everything else above it you cant navigate as quickly because things are constantly up or down moving). If things are fixed in place like they used to be you can develop muscle memory and do things quickly. If things move, you cant get that memory and every page is different and the process is slower.
Why was the selection feature changed? Click the far left box to select multiple items or click the item itself to deselect all and just select that one. I saw no problem with that feature and now when I go to select just one person I might accidentally also have someone else selected and make a mistake. I need to scroll scroll scroll till I find that person to deselect them or click the "deselect all" button then remake my selection. Seems like a lot more steps to make an option that you already had (selecting multiple) a little easier. This is particularly bad when I hit the back button on my browser because I always need to relocate the selection, deselect it, then select the next item. Every time.