With the Houston Astros' move to the American League West, the American League and National League both have 15 teams again. In one sense, this makes things more equitable, because now each team has to overcome four division rivals to guarantee a spot in the playoffs. Under the old system, NL Central clubs had to beat out five contenders, while AL West clubs had to best only three of their opponents. The more teams you have fighting for the same playoff spot, the less likely each one is to come away the victor, so shipping an NL Central team to the AL West could be seen as a move to make things more fair.
However, there's an unintended consequence to having 15 teams in each league -- mandatory interleague matchups nearly every day. Under the old 14/16 arrangement, MLB would confine interleague games to several distinct periods. Now each team has to deal with randomly dispersed interleague matchups, and this puts several NL teams at a real disadvantage.