Lots of optional things are important for seratonin. Not obligatory.

I was a zero carb power lifter for about 4 years before adding carbs back in. I had no issues. My SO runs cross country and was on the same diet as I was. No issues and regularly pushed PBs. Putting on muscle was even easier for me than a carb heavy diet. Higher energy levels too.

There are different ways to meet your chemical and nutritional needs that do not necessitate carbs. They aren't bad when consumed intelligently from healthy sources but they aren't required. Saying carbs are required is misleading.