Honestly, I am surprised, Google actually listened to the complaints of the folks who disliked the new Google tablet interface and to solve the white space problem that is incredibly noticeable on the iPad Pro - they added pinch and zoom to the interface.
So now you can pinch and zoom in to remove a lot of the white space.
AJ from Google said in the ongoing Google Web Search Help thread:
Thanks everyone for your continued product feedback! The team heard you, and pinch and zoom should now work again on tablets. Please confirm below if you are experiencing otherwise, and we'll continue to investigate internally if that is the case. Thanks!
Here is an animated GIF of how it looks on my iPad Mini:
Forum discussion at Google Web Search Help.