From Sega Retro
So there are definitely enough differences between these two Super Leagues for them to have separate pages, but the Mega Drive version is painful for other reasons.
In Japan, the Mega Drive Super League has Japanese teams. In North America (where it's called Tommy Lasorda Baseball) and Europe, it has a different voiceover and American teams instead of Japanese ones. Gameplay and presentation wise they're pretty much the same, but we've split pages before for having different sets of teams to play as (e.g. European Club Soccer/World Trophy Soccer). Difference is, both Mega Drive versions of Super League have "world" teams, so at least half the game is identical. I haven't looked into this that deeply - there may be other differences.