Many people agree on Zapdos having bad setups which is true. When it gets bad set ups first turn, thats definitely its downfall and main weakness. I really agree with Otaku stated earlier on Zapdos position in the current metagame, very valid point. But hey all decks have some way of getting bad setups including Dark Ampharos and Blaziken. If you start with Pidgey or Torchic, more than likely a Zapdos deck or whatever is gonna take advantage. Nowadays, decks including Blaze and others RELY on that turn 1 dunsparce because mainly its the only thing thats gonna save them from a lost.
Overall, Zapdos is not Tier 2, its merely the bottom of Tier 1. If you put Zapdos in Tier 2, its definitely the fastest and strongest of that category, but in Tier 1, its at the bottom because of its weaknesses to other consistent decks.