The Mets are making the correct decision in brining in the fences in Citi Field. It isn’t to help players currently on the team. It isn’t because they built a “pitchers park,” then changed their mind. The reason the Mets are bringing in the fences is to create a fair ball park. Fair doesn’t mean a balance between “pitcher” and “hitter” friendly. They are aiming to reduce discrimination against certain types of hitters. Balance means “we can bring in a good hitter without wondering how the stadium will change their production.”
Citi Field is not a balanced park, it discriminates against left handed hitters and right handed push hitters. It is all that more glaring because the Mets are currently full of these two sorts of hitters, and this inherent ballpark discrimination is, whether you’re willing to admit it or not, greatly affecting the team’s offensive potential. But Citi Field isn’t being changed because these players are on the team, and the problem wouldn’t go away by “getting better players.” That is like suggesting only people who have cavities should brush their teeth. The Mets are doing the right thing and fixing the root cause of the problem. It isn’t lineup construction, it isn’t the players, it is the stadium.
I can hear you already, you’re saying “changing the stadium wont make the team better!” Correct, it wont. It will, however, open their options. They will be more able to go after players in free agency, more able to lure players to their team (especially lefty corner players on short contracts), and it will generally increase the team’s offensive output. It will have untold impact on the development of their own players. How many players in the future will provide the Mets a few nice hits, maybe a good season for a fringe prospect or free agent, because moving in the fences turned a handful of their flyballs into homeruns? It has a bigger effect on the team than you may recognize.
You say “both teams play on the same field!” Correct, they do, but you’re making two assumptions. First, you’re assuming the Mets and their opponents hit the ball in the same relative locations. Second, you’re assuming that players who play in Citi Field have the same approach as players who only occasionally play in Citi Field. I can tell you the Mets and their opponents do not hit the ball in the same relative locations in right field. The Met opponents tend to hit the ball significantly further in right field, while the Mets tend to hit far more balls that just barely go over the fence. The Mets also hit many more balls that just barely miss going over the wall in right field.
In left field, both Mets and their opponents have the majority of their homeruns just barely clear the wall. This is the ideal. I believe this should tell us the wall in left field is fair, but the wall in right field isn’t. The Mets should move the fences in right field in to account for this, and they finally are doing so.
Regarding whether Mets players have a different approach while playing at home than their opponents, there isn’t an easy answer. Even if we could state definitively one way or another, it would be difficult to understand the causality. Organizational philosophy, player philosophy, coaching, opponent pitching philosophy, lineup construction, et cetera. But I believe there is enough reason to suspect a homefield mentality for the Mets, between player comments and the glaring difference in homerun distances in right field, that you should at least consider the possibility that the current stadium configuration is hurting the team on a psychological level.