anguswhatever
Not sure what you meant by the Left Hand Side retreating to under. For me it is still where it has been for a long time at the bottom of the Screen. It never moved unless I had the 'Coming soon' 'Try it now' on which I don't. It has to be somewhere and I think probably takes up the least amount of room at the bottom. And I would rather it take up room at the bottom (prior location before the change) than on the side. For me though the Left Hand Side was annoying because it was more cumbersome for me to position my cursor on the File Tab at the top of the screen which I do use somewhat.
By the way, The same Office Theme selection I showed you can also be done by doing:
File>Options>General where you will see the same selections on this Options Screen. So there are two ways to get to the same set of options. controlling the Office Themes.
As far as I know the Search Field has not moved and it is on the top in the Title Bar of the Outlook Window which doesn't take up any needed space in my opinion. It has been located there for I'm guessing maybe a year or so. I rather liked it better in its old location where it didn't seem to take up much space either.