Is Pinsir relevant?

Yes, of course, but please consider finding the one with a higher IV.

Yes. Moveset is more important than IV's. 80% will do fine

I have a 2300CP Pinsir with FC/XS and it is great against Exeggutors. If it's better than for example Arcanine I wouldn't know since i don't have one yet.
I'd say definitely power him up. It's fun using him and it's cool seeing him in a gym if you decide to drop him off in one.

Id wait till Scizor comes out. It will be relevant...

If it is 1000-1400cp, leave it there to use for training against Exeggutor. With the CP update though, all of my Pinsirs became too big to train efficiently, but not big enough to attack.

Im very happy with mine, it's a egg-killer with 1900 CP and 86%

My Executor with 99% IV 15/14/15 at level 2388 died quickly with executor. I find that very interesting. Everybody saying he's amazing for executor but all i see is me dodging all the dam time cause every move takes a chunck of life out of me. 2300+ executor.