I'm absolutely convinced without question that Walter Johnson is the greatest pitcher ever. Plus, Walter Johnson's 1913 season is also the greatest season ever by a pitcher, and using him from that season would be my choice as the pitcher to win one all-or-nothing game. Not only that, but in a one game situation, he'd give me an advantage over just about any other pitcher in history with his placement in the lineup since he is also among the greatest hitting pitchers ever.
The argument of having to use a contemporary player because of the modern advantages - aka the time machine method - isn't at all fair to the players of yesteryear. If I went back in time to 1920, grabbed Babe Ruth and brought him to April, 2006, he wouldn't even come close to being the greatest player in today's game. Likewise, if I sent the 2006 Reds back in time to 1920, they'd absolutely dominate, cruise to a pennant and would likely win the World Series.
While we're at it, if we transferred the Big Red Machine to 2006, they'd likely be nothing more than an average team in today's game. The Big Red Machine was dominant for their time period of the 1970s, but they'd be nothing special in today's game. They dominated 30 years ago, and they'd be well behind the times in overall baseball ability if transferred to the 2006 season.
What's the point of all that? Simply that you must compare players and teams to their peers and how well they rose above their peers.
Babe Ruth rose above his peers in his time more than anybody else who has played the game. Walter Johnson did the same on the mound. Because of that, Ruth is the greatest player of all-time, and Johnson is the greatest pitcher of all-time.
As a team, the Big Red Machine, mostly in 1975 and 1976, dominated their peers like only a few teams in the history of baseball have managed to accomplish. Because of that dominance, those 1975 and 1976 squads are considered to be among some of the greatest teams in history.