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Fortunately, I found that Wikipedia allows to select the old design in the account preferences when you're logged in. You can even switch back to the very old pre-2010 theme.
I think a big assumption of the new design is that you use it to use wikipedia itself, generally most of my wikipedia usage is as a reference for the main thing that I'm actually doing, where by having a wide modern monitor, I can put wikipedia on half (or less!) of the screen and have it be useful. Now with this sidebar thing it's much more annoying to do.