Early21 "The Standard was the guitar used by the pros back then - Clapton, West, Zappa, Garcia, etc."
I guess no one got around to telling Pete Townshend that the SG Special that he used during the Who's most famous period (1969-1974, Tommy Woodstock) was not a professional guitar. The tone that Townshend gets with his SG Special on Live At Leeds is pretty amazing, but it's a matter of taste (single coil P90's vs. Humbuckers).
I love and collect vintage Gibsons. Sure, they made some mistakes in the later 60's - early 70's and some of those guitars are not their best. However, they also made some AMAZING guitars during that period up until the day they closed the Kalamazoo factory. Everything after Kalamazoo is like a different company. The better early 70's Gibsons are probably some of the best values out there in vintage guitars.
There are some great SG's from the early 70's. The thing about SG's is that they are pretty fragile and a lot of them have broken headstocks and some of them have had problems in the joint where the neck meets the body. Sometimes the repairs have been done badly and you want to avoid those guitars if possible. I would much rather have a good early 70's SG than a new one. The mahogany in the older ones was better than what is available today and it has also had 30-40 years to dry out.