Baseball core principles are changing as advanced stats become the norm.
Batting averages, the key stat in a hitter's success, are now downplayed or discarded in favor of OBP or OPS. The league is now flooded with .230 hitters with high strike out rates because power stats are more "valuable" than a single or a single out (strikeout). If a lineup is filled with .230 hitters, it is more prone to long batting slumps. In 2018, the Cubs found that out the hard way by scoring one or fewer runs in 41 games.
No one is trying to find a traditional lead off hitter. A person who hits for high average, can work a walk, and steal a base with ease. The reason is that stat men believe a steal is a risky and worthless strategy. Teams no longer think on ways to "manufacture" a run when the trend is still the 3- run HR or bust mentality.
There are so many .230 BA strike out machines that pitchers no longer have to "pitch to contact." In other words, starters use to have to conserve energy to pitch 8 innings/start. But today, they are nibble on the corners and try to "trick" batters into missed swings. Other pitchers just rely on two pitches, a fastball and an off-speed pitch, and throw as hard as possible knowing that they are on a 100 pitch count. It does not matter if you are in the third or sixth, at 100 you are going to get yanked. So wins, an old measure of starting pitcher success, is another meaningless stat in the modern age. Pitchers don't have the mind set to go out a "win" a complete game because management has diminished their role by bolstering the bullpen to finish games. It also is driven by the fact that pitchers give up more hits the third time around in the batting order. So teams are planning to get a pitcher, however effective, out by the time the batting order rolls around for the third time.
All the nibbler pitchers have increased the time of games, and contributed to the wide variance in strike zones called by umpires. In the past, a quality pitcher will blister the zone with his best pitch challenging the hitter to hit it. Now, batters are sitting back looking for "a mistake" to hit. Since the pitcher has the advantage, most do themselves no great service by throwing outside the zone.
Traditional pitching coaches preach that it is not velocity that matters most in pitching, it is movement. But velocity speed guns are still the primary tool to evaluate pitchers. A 100 mph straight fast ball can be hit by any major talent. It is the 94 mph pitch that moves sideways or plummets down that causes batters more problems. Bruce Sutter was an ace closer not because he had a dynamic fastball, but because he developed the original fork ball, an enticing pitch that looked like a heart of the plate fastball until it dropped off a table at the last moment. Sutter was looking for swings and misses, but he could throw his fork ball for called strikes. He was a pitcher not a thrower.
A pitcher has a plan for each batter, because each batter has a hole in his swing. A sinker ball master can have opponents beat the ball to the infielders for easy outs. Such a plan limits the starter's pitch count and gets the entire team into the game. A thrower gets on the mound a rears back for every pitch. He does not really know where it will land because control is not his primary principle.
With all the new stat analysis, what is lost is the more basic elements of the game: runs and outs. Each team has 27 outs to score runs. How you use those outs to get runs is important. A "productive" out such as a sacrifice bunt, hitting to the opposite field, a sacrifice fly are all downplayed today. Teams have horrible collective stats with runners in scoring position. Why? An individual stat priority takes precedence over the proper situational play like moving the runner over, of choking up on the bat to hit a single instead of a home run. Scoring runs should be the priority of every player, but there is now an inherent bias to put individual stats (that's how players are paid) ahead of the team.
Front offices continue to hire cheaper, non-old school managers who management can control more with stats than gut strategy. The game is morphing into a video game without controllers.