Is Pinsir a Viable Attacker?

I'd use it to prestige against Exeggutor.

Wow I love your Pinsir...it's a great attacker against pkmn weak to bug...so especially exeggutor

Yeah, you have a good one. Depending on it's CP, I'd either leave it as is as a prestiger or power him up a little as a Exeggutor slayer...

Depends how you attack.
If you're a spammer, I think you'd be better off with a poke with higher stamina and a more useful moveset.
If you're a dodger, then it might become useful in specific situations vs. psychic and grass (no dark yet).

Overall, still a fun poke to use due to its novelty.

Yes, I have had success with the identical Pokémon, a Pinser with IVs of two 15s and one 14 (although I don't know in which order), and the same move set. I use it to attack Exeggutor, which is double weak to bug moves and is prevalent in gyms. One of the key reasons I use Pinser is that Pinser resists grass moves. Two of Exeggutor's charge moves are grass moves, so your Pinser has a two-thirds chance of resisting the charge moves. That is a pretty good move set and resistance set combination. (Pinser is neutral to Exeggutor's two quick moves and third charge move, all of which are physic moves.) (Best Pokémon may be Scyther, with Fury Cutter and Bug Buzz, because Scyther is double resistant to grass moves.) My Pinser is CP 1807 at the moment (though I power it up as I go along), so it kills Exeggutor pretty handily up to about CP 2200. Beyond that, I switch to a beastly Arcanine to kill the Exeggutor.

I am of the view that the Pokémon you use to attack depends on your style of play. I like to play what I call a "finesse" style where I use the lowest CP Pokémon that can do the job to attack. A good quality Pinser (which you have) with the right move set (which you have) is a great finesse attacker into Exeggutor.

Against Exeggutor, yes.

Against anything else? No. Fury Cutter has very bad DPS.

Fun niche pokemon to prestige / attack against Exeggutor. But the low HP makes it not that useful beyond that.

I'd use it only against a gym that has 2 Exeggutors; you should be able to get through both if you dodge. Against any other mon typically found in gyms, Pinsir is terrible.