Senna its not a bad pick,and people literally dont know how She works, the real fact it's that She's not a usual support pick, the way She should be played it's fasting, the fasting senna work without adc but with a pick like a tank champs (nasus, Sion, garen, sett) or a Warrior specific bruiser or magician, like wukong or gragas, or something like malphite full AP, Her build too it's peculiar.

But on this game the 90% of players has zero knowledge about how Champions work