It is more diverse of you think in terms of Southeast vs East Asian looks.
There are SGO members who would fit into the lineups of AKB or SNH and others who look more like the girls for BNK or JKT.
Most girls in BNK or JKT could easily fit into AKB or SNH lineup tbh. They all follow the same East Asian (particularly leaning towards Japanese aesthetics) beauty standards of fair skin, big eyes, etc.
In this regard, I'd say JKT & MNL seem more truly diverse, since they have the biggest mix of EA & SEA looks, whereas SGO & BNK tend to lean more East Asian.