Having a maxed stat comes into play in the final chapter. For example, you will NEED 20 valor to beat Otton in a sword fight if you choose to go that route, because that is what is required for what is essentially a once-in-a-lifetime feat, a human defeating a trained arknian in single combat.

You won't need 20 if you have grandfather's blessing and engaged in the family rite as his spirit will help from beyond the grave.

It's better to have balanced stats when you go to the capital and build up your stats over your career.

I developed the valor over time and had 20 towards the end of my life. I didn't need to fight Otton in a sword fight and used other tools as a judge. Still, you think that it would have been useful in a few other earlier skirmishes in the judge arc.

I had 20 Valor and just got skewered in the judge's hall so that probably is either a narrative logic paradox or incorrect checking of that stat.

You can get 20 valor and still die to a pack of assassins or trying to surprise an angry, distracted noble in a duel, and essentially never make it to where that choice actually matters.

The phrase 'valor is most important to the judge' could use a rework even if that isn't an implication to ignore all other considerations (but to be fair I play almost exclusively on ironman mode with choices hidden)

Valor 20 is kinda useless since you can also defeat Otton with 18 Valor + 10 willpower, but valor practically levels itself up anyway. And Diplomacy 20 is used to get Otton and El Borne to team up if you went for Career 10.

This means you don't get to use either level 20 skills if you play rebel nobleman.