Actually, he came into a decent environment in Buffalo (he still resides in the area, btw). The Sabres were only a few years removed from a Stanley Cup Finals appearance, with many of the same players still on the roster. Bowman definitely put his stamp on the team (subsequently drafting players such as Barrasso, Andreychuk and Housley). However, not everything can should be pinned on Scotty for the Sabres's lack of success. Other championship-winning GM's had come in (Punch Imlach and John Muckler) and weren't able to lead the franchise to the Holy Grail either. During the mid 80's, some Sabres fans used to say that putting the blue and gold on led to an increase in estrogen levels.
The book you read was spot-on in its assessment. In St. Louis, Scotty had a bunch of Habs cast-offs (Al Arbour played defense there too), in a conference full of expansion teams. Many teams in the Eastern Conference would've been more deserving of a trip to the Finals than the Blues. In Montreal, he got to coach a team of future HOFers. In Buffalo, the results were *mixed*. In Pittsburgh, he inhereted Bob Johnson's squad. The Red Wings were on the verge. So, there's a point of view that the coach/GM has to keep egos in check, create the right chemistry/winning environment with the right personnel decisions. More often than not, he did that.