He's not 'evil' and hyperbole like that's fueling dangerous levels of discords.
I saw the footage of the police kicking the offender in the head (one officer did it repeatedly, 3 or 4 times, the other did it once). It is serious and I interpreted it as the officers being out of their depth because of lack of training/experience so resorted to blunt force (and swearing) - an emotional response rather than demonstrating control and knowledge of how to disarm someone. I don't blame them for that - they're normal police officers, not firearms officers. You can practice using a taser against a pretend suspect but it won't prepare you for a real life situation you might face only once in your career.
How should officers disarm someone lying on the ground after being tasered? I don't know and it's obvious those officers didn't know either. Perhaps hitting the suspect's arm with a baton? But kicking the offender in the head certainly isn't the right method and the Met should review the training they give their officers.