Trainers use semi-competitive strategies, including held items, Mega Evolutions (starting from Wattson), and Pokémon with Egg Moves.
If you are tired of steamrolling through Gym Leaders with a single over-leveled starter, RR/SS offers the remedy.
Pokémon Rutile Ruby and Star Sapphire (RR/SS) are high-difficulty ROM hacks of Pokémon Omega Ruby and Alpha Sapphire (OR/AS) created by Dio Vento. These hacks are designed to provide a much more challenging experience without altering the "core" Pokémon lore, meaning types and movesets remain largely vanilla.