I think that regardless of anything else, we can all agree that releasing Roar, Dark Horse, Walking On Air and Unconditionally all within two months of one another was a terrible mistake. They just didn't anticipate Katy's promo single overshadowing the actual second single like that.
They better learn from the next era to keep as much of the album a surprise as possible until they want them to hear it. Then see which album tracks the GP respond to the most and release them as the singles.
I would honestly be fine with having only one single before the album.