Ziggs is a really strong counter pick in this meta.
The main ADCs are immobile. Jhin suffers worse than Ashe or Sivir due to his ult being a gigantic, "Insert ultimate here." Sign.
Ziggs outranges the immobile, meta mages Vlad, Viktor, and Cassiopeia, meaning he gets a pretty free lane to farm safely in considering the two champions only do really well against opponents they can stay in range of and kite.
The best support can't do shit to mitigate his ultimate to protect his carry.
And these sound like qualifications for just about any long ranged mage, right? What sets Ziggs apart from Lux or Xerath?
Objective control (mainly towers). Due to the first blood tower bounty as well as his better overall objective control than Lux and Xerath he is a far better champion in the meta. I watched my buddy yesterday take the first, second, third, fourth, and fifth tower in a game because of a combination of Ziggs' poke, passive, and Satchel Charge execute.
Of course, Zed is still alright. Kat's pretty ok, and LeBlanc gets some decent play time so he's still just a counter pick, but in a good matchup with a Jhin being the enemy team's ADC and he's probably the strongest midlaner at the moment.