Sandslash and Quagsire are workable counters to Pinsir, as is Intimidate Hitmontop (Pinsir will be forced to run Mold Breaker due to Weezing). Pinsir has decent speed, but not great, so it can be revenge-killed rather easily.
Both Sandslash and Quagsire are not not good counters as both can be 2hkoed after a Swords Dance while neither can OHKO.
Really, if Pinsir is BL, so should Aerodactyl. Pinsir is just as easy to "wall with prediction", but its speed allows it for several Pokemon to revenge-kill it. Its defense is decent but its SpD is anything but. Its HP is also rather low, so it doesn't have an easy time switching in, and Stealth Rocks only further this.
Aerodactly and Pinsir have nothing in common aside from a Stealth Rock resistance and an occasional move or two. What does Aerodactly in UU have to do with Pinsir being in UU? Also, Pinsir isn't exactly slow and it has better defenses than Aerodactyl while retaining the ability to boost its base 125 Attack through Swords Dance or Bulk Up. When Pinsir was banned initially it was a pretty mutual agreement that it was too strong for the tier due to a number of factors and the Pokemon added to UU don't exactly change that in any way.
Anything with 296 or more Speed that can also OHKO Pinsir, while resisting or being immune to the attack that Pinsir will likely use on your current poke, is a counter. Choice versions are harmless if you can predict right.
I'm not going to bother picking down your whole post again so i'll just comment on a few things that really hurt your argument to bring down Pinsir.
The definition of a counter is a Pokemon that can switch into any move of the Pokemon that it is trying to counter while posing an immediate threat to that same attacking Pokemon. What you suggested is not a counter, and for what its worth there are not a lot of Pokemon in UU that fufill those requirements. Also remember you say the move Pinsir is
likely to use, If Pinsir uses another move then you might have just cost yourself a Pokemon. Also, Choice versions of pretty much any Pokemon are worthless if you can always predict their move so that won't really convince anyone.
Improve its Defense, Speed, lowers its HP and lower its Attack and you have converted Rampardos into Pinsir. They're basically countered by the same kind of poke; fast revenge killers or if you're decent at prediction, stuff that resist what they're throwing at them while OHKO'ing back.
Lower Typlosions Special Attack, give it a bit more Attack, raise it's Speed a bit and alter its moves a little then you basically have Rapidash. C'mon you can do this for a bunch of Pokemon, it's not going to change anything. Rampardos and Pinsir aren't countered by the same Pokemon and and don't randomly throw around the term prediction as if every set will be a Choice set. If you review the previous thread for why Pinsir was actually banned it you would see it was mostly because of the Swords Dance variant.
I agree that if Aerodactyl is dropped, Pinsir should be reconsidered.
Still, this should be a moot point as we should be unbanning them all anyway and building this uu tier right this time.
By right I mean with experience. I don't need objective reasoning to ban or unban something; subjective reasoning is fine for me coming from an experienced individual.
As I stated above I don't see what Aerodactly dropping has to do with Pinsir returning or being reconsidered, they are completely different Pokemon.
Also what most people don't seem to understand with regards to dropping all of BL into UU and testing them is that it will be a Smogon wide project and not relegated to only the members of this thread and as it stands UU is very low on the list of things to be considered. And even if it's done it's more likely and probaly a better idea to have it implemented on a secondary ladder as this is a process that will take months to finish and this way we can go about it without actually upsetting the current UU metagame.
The order of things to be done is listed below and as you can see UU really isn't a top priority at the moment. Little changes here and there can be made to the tier but something as big as merging BL and UU will most likely have to wait until the other things in the list below have been sorted out and dealt with.
1. Garchomp (75)
2. Lati@s (116)
3. Evasion Clause (126)
4. Manaphy (127)
5. Species Clause (136)
6. OHKO Clause (150)
7. UU Tiers (158)
8. Mew (159)
9. Arceus (172)
10. Darkrai (176)