@machmans: Actually, with Speed force Barry can steal the speed anyone. once he does that he speedblitz Birusu.
Speed Force also allows him to tank heavy hits and he IIRC he is so fast he can be everywhere at once, IIRC he is fast enough to time travel...I do not see Birusu doing that.
Also Buu won't be destroying anything since Flash speedblitz him and Flash can escape the planet.
Speed Force also grants him flight I believe.