I don't think S6 is worth talking about much, it should be, because it probably the best start of any Buffy season..... and yes the start of S7 was not bad , selfless stands out and conversation with dead people one of my all time favourite....but after that to much like the spike show and to little like BTVS
The Willow drug stuff is the rough patch of S6. Plus I don't like the Big Bads. But it ends on a high. I think the Dark Willow trilogy is very good. It sort of picks up again by the end of the season.
Selfless is even better than CWDP I'd say in S7.