Now that a generally reliable leak has indicated that Pokemon Ruby, Sapphire, and Emerald are coming to Switch consoles in late September or October, it's worth pointing out that Pokemon Sapphire is likely to outsell Pokemon Ruby. Of course, Pokemon Emerald is the special Third Edition, and it will likely outsell its two predecessors, but when looking at the two OG Gen 3 games, Pokemon Ruby and Sapphire are the prime example of a long-standing trend.
