I reached the stats cap on both attack and defense and I do 3 damage to the digimon of the challenge Aro's death commisioner and he deals 4k damage with every attack so it is impossible to beat so would be nice to make the stats cap higher otherwise it is impossible. Also I think 50 free battles is too much to change the challenges list I think 30 would be a more balanced number. Also the game is great I love the details and design of the digimons and everything.
This is the proof that it's not impossible. You can count it as the ultimate challenge to really challenge your digimon.
I genuinely hope that the dev will add more of this kind of challenges or maybe add "Nightmare Battle Mode" where you can't do 1 hit kill anymore and have to use items properly in future update so the game wont get boring easily. Also, with that kind of challenge, you will have a reason as why you have to grind your digimon stats to the cap.
Also, the new mode should pay attention to digimon type, so when you use the right type to battle, you can get significant boost damage ( for example, without using any items 3 damage will become 6 damage if you use the right type of digimon. And with using items that 3 damage become 4k damage, while with the right type of digimon 6 damage become 7k damage).
Eventho your digimon still will never do the 1 hit kill in that battle, but at least the right type give you more advantage to win the battle so this will become more reasons for player to raise more digimon from other types.