That is one way. However those players have a higher fail rate then someone who can actual hit. Take burger. They drafted solely based on his EV being one of the best in the nation. He has become an MLB player. This is a win as the vast majority don't.
All teams need players who are good at both they are just really hard to find so they try to blend both.
I'm not disagreeing with you ,it just not as easy as "draft or trade for players who are both good hitters and good at defense."
For years KW drafted athletes and was soundly ridiculed for not drafted baseball players. When the farm system didn't produce they switched to drafting baseball players. He was then knocked for not getting the impact athletes.