Wide Game Mechanics
When we talk about deep or wide mechanics we do not mean the common play style of playing tall or wide.
I usually look down upon wide game mechanics and call them often "gimmick mechanics". But to better understand the difference between a wide and deep mechanic lets look at some concrete examples and abstract onces.
Defining Wide Game Mechanics
For me a wide game mechanic is a mechanic that has little connection to other mechanics. The worse offenders here are mechanics that take time and resources to interact with but have little real impact on the overall game. How do you see them in game? Wide game mechanics are often shown in a separate menu, with separate buttons and values. Sometimes these new values are added after a DLC release. Before puppets of your empire where just puppets with some new interactions now with our new wide game mechanic they have a new resource called loyalty, and you have new buttons to press to increase or decrease set locality for bonuses and malus.
This common trend of adding new resources and buttons to interact with them for a bonus or malus (trade-off) is a common occurs in modern paradox DLC design.
We may redefine a wide game mechanic as a shallow one. But why I am not doing it? Because the reality is that most implemented wide game mechanics are quite large in "content" they add.
Another Example Victoria 3 Cultures
In Victoria 3 there exist many different cultures (302!) and each culture has their own two culture traits (over 60 different traits!). They have a citizen system where depending on accepted culture the people living in the nations have different privileges. Cultures even effect what goods they prefer to consume. But in reality while playing the game you won't really feel the differences. The wiki entry gives the feeling of "ohh, so cultures are quite deeply implemented". But in reality its nothing more than a wide game mechanic. Cultures touch many aspects of the game but have little impact on it. This is the prime example of it.
Another Example Crusader Kings III: Coronations
In the new DLC for CK3, you get the ability to make an oath. basically if you fullfill mission X get Y amounts of bonuses. Around 8 can be choosen. They are all a mix out of boring, uninspired or simply broken options. Instead of 3 really interesting options we get padded out content to sell something. Paradox needs to learn how to market and sell quality. As of today paradox only has the ability to market and sell quantity.