You are missing a very glaring detail.
Vanilla wasn't just one patch bro. 1.12 was the most balanced. Thats why its used by private servers. That is why its being used by blizzard.
Would you want 1.0 where using the spirit rez meant 100% durability loss or 11.1 where it was lowered to 25%? They also removed reagent costs for mark, fort, and ai. There was no maraudon. No option to hide cloak / helm. No Gurubashi arena. How about starting at 1.3 which added DM, Meeting stones, dungeon player caps? Good? Alright!!!
Okay lets go with 1.3. Whoops, no Priest or Hunter quests. No honor system either. No? Sounds bad right? Fine fine, lets go 1.4 so we have these things. Oh shit. Guess what? if we go 1.4, we dont have battlegrounds! Nor do you have BWL, Darkmoon Faire, or the warrior / warlock talent revamps. You played a warrior? You really want 1.5 so your warrior is way more useful? You want to kill Nef in BWL? Sweet! Lets skip right to 1.6 so we have battlegrounds, new raids, AND a couple revamps. I play a hunter though. Why would I want to play a version of the game where im gimped in certain things when they did a revamp for my class in 1.7. I say we go with that one. I mean come on bro, Id love to experience ZG and Arathi Basin again. Good. 1.7 it is. Thats final!
... or is it?
I just remembered something. AQ40 was probably my favorite raid. And my main was a Holy Pally. AQ was released in 1.9 along with the Paladin revamp. Id much rather that be the base for classic.
On a more serious note. Do you see the problem with trying to decide on one patch or the other. Lets be real. Anyone with a 1/4th of a brain minimum knew that they were NEVER EVER EVER EVER NEVER EVER going to release cyclical patches. They were always going to pick a patch and roll with it. They without a doubt picked the right patch when it comes to picking one where things are the most balanced. As balanced as they could be anyways.
The ball is in their court. They better re-tune content around 1.12 or just stop now.