If Comcast can hijack our democracy and wield the state's power against public interest, then what's to stop it from hijacking our democracy to increase the state's power in the first place? How does creating a city-owned utility in any way change Comcast's lobbying position? Monopolies can and do form and persist without government intervention. The textbook example of this is utilities.
Finally, if creating a city-owned utility is beneficial to Comcast, why are they vehemently against it?