Gestalt Characters

[Turcano]

Your example of Mystic Theurge and Arcane Hierophant are not applicable since they are combination classes and are forbidden under gestalt.

Well, I did say "personally." And the reason why combination prestige classes are not allowed is because people would normally interpret the bonus caster levels/sneak attack/etc. as stacking. If you interpret them as overlapping, there is no real advantage to taking them other than for the class features that the prestige class itself provides. For example, if a player was playing a rogue//wizard gestalt and wanted ranged legerdemain really, really badly, I would see no problem with letting them become a rogue/arcane trickster//wizard and ignore the spells/day bonus (since it overlaps with the normal wizard progression). In retrospect, the mystic theurge was a really bad example.