Well they weren't very good at it then. If they scored 10 runs every game and won in sweeps and blowouts, don't you think the evidence would be a little more supported?
Baseball is inherently difficult and a game of failure. When a great player fails 70+% plus time that is proof positive.
Even when you know what is coming and hit it well it still needs to find some green.
When teams are so even even a slightest of edge can be enough to push you over the top.