I also thought reborn was easy at first, but dont worry it will get harder
Heres a list of battles in Reborn that you likely will have trouble with if your not prepared, as many people also have trouble with these battles, so look foward to these battles if you want a challenge.
No spoilers really, I dont list the trainers names just what the battle is, like the gym type they are
- 1st and 2nd "Gauntlets"
-Fire Gym
-Ice Gym, its all RNG, you'll see
-Fairy Gym
-Water Gym
There are probably a lot that I missed
Also keep in mind, where you are in the game right now, the important Trainers Pokemons are not fully EV/IV Trained, they will be EV/IV trained as you get later in the game, I believe it starts in the Fire Gym where they are fully trained, that combined with everything else that goes on in that gym