Zapdos

Of the initial 3 legendary species released in Pokemon GO, Zapdos was arguably the best at the time. But the introduction of Raikou dethroned the avatar of Team Instinct, and it's slowly slipped farther and farther into obscurity with each passing generation. It's still a viable Electric Type attacker for sure, but it's not a top-pick for the role any longer.

Zapdos’s Flying typing gives it an advantage in a small subset of matchups, but the extra weaknesses, particularly to the Ice Type attacks that Water Type raid bosses frequently carry, can render the dual typing more of a curse than a blessing.

Best PvE Offensive Moveset

• Thunder Shock* has slightly more DPS than Charge Beam, but it might not be worth spending an Elite TM on.

• Thunderbolt is more flexible and consistently outperforms Zap Cannon in relevant match-ups.

• Thunder's low power renders it the worst charge move.
• Drill Peck does benefit from STAB, but doesn't really synergize with Zapdos' fast moves. 
• Ancient Power has no use on Zapdos. 
• Return is basically worthless.

The legacy Thunder Shock performs better than Charge Beam due to faster energy gains. 

Drill Peck fills a dual role here, both as Zapdos's cheapest move (enabling baiting) and just as a solid STAB move. Pair this with Thunderbolt for the most consistent Electric damage option. If you're feeling spicier, consider running Drill Peck + Zap Cannon. This leaves you significantly more reliant on careful baiting, but if you can land it then there's no better nuke in Zapdos's kit.