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Emerald was more or less an upgrade from R/S
Gym leaders? They got more pokemon and had a few extra levels under their belt and you had Juan
Pokemon? Arguable since there still some exclusives but you had a good selection and some newer ones
Trainers along the way? Buffed a bit so you didn't go against a gym leader who was level 28 and the trainers highest is 22
Antagonists? You battled both and it was more fitting plan and base-wise, a.k.a magma by the volcano and aqua out by the sea, rather than one takes on both and the others seen as the 'good' side
Elite Four had some extra levels on them too
And of course the post game content, frontier being the main thing, you also had Steven at Meteor Falls in the back who was really high levelled
