I have to agree about the over greasing/oiling of boots. I really enjoy his channel on YouTube, but I feel Wranglerstar over oils his boots. Like skin, leather can also be over moisturized, too much and you run the risk of it tearing or loosing it's structural integrity.
I've cleaned, restored, resoled a lot of different boots. Leather is resilient and holds up to a lot of abuse. Dish soap is not going to harm your boots. These boots were covered in grease and grime. I cleaned them inside and out with hot water and palm olive soap.