Bringing in Ventura was a bad decision (he threw 73 pitches 2 days before, not the day before), but taking out Shields wasn't the worst call ever. I'm not sure why he didn't bring someone in from the pen, especially as dominant as it's been all year....but pulling Shields wasn't the issue...it was who he brought in.
And every coach makes decisions like that when it comes to pulling pitchers...if they leave the starter in, they get lambasted for doing that. It's a thankless job most times. What no one seems to be bringing up were his decisions to keep running, running, running all night on the backup catcher...the stolen bases are what brought them back into that game and eventually won it for them. He put an awful lot of pressure on Oakland with that. He gets no credit for it somehow.
I'm not saying he's the best manager in the game, but he's surely better than an awful lot of managers...some of them are still coaching in the post-season as well (Mattingly comes to mind for one).