This blog post didn't really do much for me. The blog author's definition of system is not how contemporary game development community uses the word. We wouldn't call decks of cards "systems", they're just game pieces. Systems are things more like "economy" or "crafting" - networks of mechanics working together.
https://www.amazon.com/Advanced-Game-Design-Systems-Approach...
This blog post didn't really do much for me. The blog author's definition of system is not how contemporary game development community uses the word. We wouldn't call decks of cards "systems", they're just game pieces. Systems are things more like "economy" or "crafting" - networks of mechanics working together.