Just to give you the flip side of the coin, doing away with the rear axle pivot both reduces weight and increases lateral stiffness of the rear triangle. IMO this is more progressive than prehistoric. Flexing seat stays are fine for lower travel, but certainly not ideal for longer travel, at least not without an obscenely high leverage ratio. As for the bottom bracket, yeah, PF can be prone to creaking, however I've found relief with the wheels manufacturing threaded pressfit BB. The mid tube is threaded, and forms a single solid BB tube, and has eliminated every hint of a creak from my cranks. Best 55 bucks Ive spent in a long time.
Another issue with the FS27 and FS29 is that youre effectively limited to 100mm rear travel. At least until someone finds a trunnion shock that will actually fit these bikes.
Anyway, after putting four or five hundred miles on my CS-FS27, you'd have a hard time convincing me to go in a different direction.
