Skill isn't the main issue, he's just inane and impractical now.
He does not, WILL not act as an initiator now. Maybe if the teamfight's already well under way you can do something, but no, you DON'T go i
His Q and R actually doing anything predicates on the enemy team NOT doing anything like simply moving a little bit, turning around and unloading on you while you uselessly run away or toward them to try to even land the FIRST Q on something.
I think the intention was to fork the enemy team on either focussing your passive blobs or your team while your team presumably jumps in to lay the smackdown and you hopefully survive to reform and ult in the middle of it.
But you need to be pretty strong to even matter in this capacity either way. GOOD LUCK getting there with this useless set of abilities in the first place.
Zac is completely team reliant and simply outclassed by everything else in the game now.