Pinsir's weakness in Pokémon GO is the same as other bug-type Pokémon, and if you face it in a raid, get ready to pull out the big guns.
Even though most trainers will be using this time to catch Sinnoh based Pokémon, you can still catch other generational Pokémon including Pinsir.
Pinsir's Weakness in Pokémon GO
If you want to defeat a Pinsir, use fire, flying or rock-type Pokémon. Although, be careful when using rock-type Pokémon as Pinsir can learn Rock Smash, a fighting-type move. If you want your safest bet, keep with fire and flying.
Pokémon GO has a busy February planned and a few events have already started. The Sinnoh event is currently live, which has pushed Pinsir out of the raid circulation. The event began at 8 a.m. local time and is scheduled to continue through the weekend, ending Monday at 10 p.m. local time.
It might make a return once the event is over, but it also could be some time before we see the return of the classic bug-type king.