It's not worse because it didn't injure him on this occasion. It had the potential to, which makes it worse. Just because Pennant has got lucky and suffered no injury is completely irrelevant to the severity of the challenge.
Well it does because all we can say is Essien could have broken Pennants leg but then you can say Rooney could have not swore at the camera. The fact is Rooney went through with his action and nothing more came from Essiens.