Just because they are his favorite archetype of cards doesn't mean he knows how to run them proerly. My favorite archetype is Karakuris and I can admit I don't run them right and my deck sould be better, I just play quite a few other cards games with more people to play against then Yugioh so most of my money for gomain goes toward them. But anyway yeah follow the banlist and you need to be consistent, running only one of a single card if it isn't o the list at all is kinda dumb (no offence). Try running 3 of the creatures you need, if your going for Rank 4 XYZ summons then Gogogo Golem is a good card, Number 39: Utopia is a staple in decks that use XYZ's. So try and make it more consistent, which in the long run will make the deck more lthal in general. and if your worrying about a certain type of deck use the Sideboard to the best of your advantage.
Huge Overwatch fan