1) I don't agree, hooking someone and killing him then backing off, even with taking damage and "feeding their ult", is worth it. Otherwise Roadhog would be absolutely useless.
2) No, he was gone the previous patch (before the one we're playing on right now), he's effective against at long range, expecially considering the lack of Widowmaker and Soldier 76 in the current meta, who previously were good in filling that role.
3) If played correctly Genji is the carry with the most potential, easily.
His mobility, his shurikens doing full damage at any range (if I'm not mistaken), and most importantly his ultimate which can get team wipes, or at least 2-3 kills consistently, make him an absolute beast in good hands.