So I don't think there is any evidence that swinging for the fences is having an effect on balls in play, unless you mean players are striking out more as a result, but if that's the case then you agree with me that strike outs are the problem and we have different ideas as to the root causes behind the increase in strikeouts. I suspect both are factors but I think pitcher dominance is a far bigger problem and easier to solve for.
First we need to understand the issue we are trying to solve. Runs per game fluctuates year to year but there isn't a trend for less runs overall. Going back to 1979 the average Runs Per Game per season is 4.53. In 2020 it was 4.65, 2019 4.83, 2018 4.45 and 2017 4.65. It was 4.46 in 1979, 4.29 in 1980 and 4.00 in 1981.
The issue I think most people agree is the lack of balls in play? I didnt want to check every single season so I took a look at the trend since 2009, and also a snapshot every ten years prior to 2009. In 1979, 76.9% of all plate appearances ended with a ball in play. In 2019 that had dropped to just 64.9%.
The trend has been more dramatic in recent years, From 2009 to 2016 it dropped from 70.4% to 69.43%, but has since fallen to 63.9% in 2020.
There are four ways a Plate Appearance can end without a ball going into play (though I'm not goign to pay attention to HBPs). A strike out, walk or home run.
Walks haven't changed much over the years. 8.5% of all PAs ended in a walk in 1979 and it was 8.5% in 2019. It did end up at 9.2% in 2020 but it was 9.4% in 1999. Home Runs have become more common, increasing from 2.1% in 1979 to 3.6% in 2019. However the big shift is in Strikeouts, which were at 12.5% in 1979 and grew to 18% in 2009 (+546 basis points), and to 23% in 2019 (+500 basis points).
It is clear to me that Strikeouts are the problem. I can see that the hitters appreoach is likely a factor here, but I think the hitters approach is a reaction to rising fastball speeds, increased spin rate and general dominance from pitchers. Its a chicken and egg situation as to which precipitated the other though.
If we make changes to the ball that lead to less home runs then all that will likely happen is a reduction in overall run production. We have seen that despite increasing strikeouts, runs have stayed relatively consistent. Teams are producing the same runs, with less balls in play, thanks in part to home runs. Reducing home runs will lead to a slight increase in balls in play, and given the fact that BABIP is so consistent, some of those will turn into singles and doubles but it will do nothing to slow down the strike rate as we see more and more pitchers throwing close to or in excess of 100 mph and more specialized pitchers.
I say lower the mound, push the mound back, do whatever you can to reduce the effective speed of a fastball as it approaches the hitter. These changes have been made before, there is no reason they can't be changed again.