Not just think! Studies have shown that ralts have indeed adapted to the sunlight of the region. You see, the sun in Orre tends to be a bit harsher than elsewhere (as it’s predominantly a desert region). Most pokémon, including standard ralts, are hardy enough that living in these conditions hasn’t changed them drastically enough to be noticeably different than their counterparts from other regions.
However, it’s true that ralts is naturally a physically fragile species, and their shiny forms are more so thanks to the genetic mutations whose side effects result in their alternate coloration. Thus, a shiny ralts from any other region would literally wilt in the Orre sun. Meanwhile, ralts born and bred in Orre have adapted to the region’s harsher weather, and as such, these adaptations may carry over to their shiny forms. That is to say, while you might not notice any differences between an Orrean standard ralts and one from another region, you will notice with a shiny ralts born from Orrean parents: Orre shinies produce more melanin in response to the sunlight, leading to their distinctive violet color.
Before anyone asks, these ralts are otherwise identical to those of other regions, so this is not considered a regional variant, no.