The subtypes work in any campaign.
And the subtypes are put in place so the Eidolon will fit into a fantasy worlds mythology not just for reasons pertaining to game balance.
Except where they really don't, which could potentially be just as many worlds as the ones that they do. Especially with the focus on outsider subtypes, my personal world is not a good fit with the new setup, as outsiders, regardless of alignment, are heavily discouraged by the remaining gods, while the old one worked perfectly given the long history of war and conflict in the world that only just recently ended. I play in another game under another DM where the same basic issues would come up if we were playing PF instead of 3.5; the old system would actually fit reasonably well while the new one would create massive headaches for player wanting to use it roleplaying wise. In Golarion through PFS play, the new one probably makes more sense, but Golarion in home games has plenty of room for the old interpretation as well.
My personal inclination is to allow either, but the choice must be made at 1st level; that way, a player could use whichever one fit their concept better, and the choice also impacts the roleplaying aspect of how the rest of the world reacts to them. Even then, I would probably allow all subtypes to be of any of the base forms and possibly ease up on the alignment restrictions. Even with expanding subtype options, the new way is not inherently any better at explaining the eidolons than the old way; they both have strengths and they both have weaknesses. Hopefully, we ever see another version of summoner again, it will find a middle ground that allows both interpretations equally well rather than absolutely forcing one over the other.