>>49849420This is accurate. Fairies can be a lot of things, but their main common feature is being otherworldly in their sense of behaviour and morality. Clefairy vs. Chansey is a pretty instructive comparison in the context of Pokémon. Both are basically benevolent, but one avoids humans in the wild and dances around under the moon and drinks dew from the grasses, while the other is very anthropophilic and hangs around human settlements helping us in hospitals. They’re mischievous and playful, as represented by moves like Baby Doll Eyes, but they’re not really evil or good in the conventional sense of what is good for humanity because they’re nature spirits. The Fairy type has always been very clearly conceptualised.
>>49849681Psychic type has served as the effective light counterpart to Dark type since Gen II. Pokémon isn’t going to present an entire type as good or evil—even its so-called Evil type—which is why Fairy is more effective at filling the niche than Light. Light would be both redundant and less flexible than Fairy and Psychic already are.