Personal experience over 25 years. Hitting each muscle only once/week gives me a lot better results than twice/week.
So I hit the gym 6/week, only one bodypart/day.
Ofcourse I also benefit from seriously targeting only that one muscle on each given day.
In addition it is for me, mentally much easier to head to the gym knowing I´m hitting only 1 muscle.
I get sore overtime I up the weight, or change exercise.

This fall I will experiment with hitting each muscle once every 2 weeks.