>>43837838usum have a very good selection of legendaries, only thing that sucks about the legends in particular is that some are locked behind having two other legends (Suicune, Giratina, ect) which are version exclusive (Entei/Raikou for example). so if you really want to go for them you better play the game twice or hope and pray a used copy hasn't caught them already (same with UBS but you don't need two to get a third one, they're just exclusive).
i know it was the same in ORAS but at least that game didn't bombard you with cutscenes 