Right, and I addressed that. If the player essentially needs to be a pro and/or the team needs to be as such for Zen to be usable then, IMO, that isn't a very well designed character. I don't see how a character handles in the hands a pro gamer matters as opposed to the average player.
I've used him pretty effectively during the beta and I'm by no means a pro player. He is clutch at pushing or defending objectives with his ult, which effectively makes his entire team untouchable for 6 seconds. I have won games single handedly by popping his ult at crucial times, turning the tide of a fight.
His DPS is also incredibly high. He can melt tanks, as long as he stands far enough in the back that they can't get to him. His heal-over-time can keep low health heroes like Tracer and Reaper going for ages, and Discord basically takes an opponent out of the game, because they either get killed or they have to run away and break line of sight.
He has a lot of utility and high DPS, which is why his mobility is low. If you can't position properly then yes, you shouldn't play him. But if you come up against a good Zenyatta, you'll see that he brings a lot to the table.