I don't see ICS about the number of cities since each game have different placement rules, in Civ 3 you only need 1 space between 2 cities, in Civ 6 it is 3 spaces. I see ICS about trying to maximizes the amount of cities possible according to game rules and that is something I see many people doing in Civ VI. Civ V have same placement rule but in V people tend to settle cities more far from each other to increase the potential of each city.
Civ 3 is tricky, you want basically a core of cities placed quite optimally due to how corruption work but very corrupt cities you have good reasons to place ICS style, Civ 6 however don't really have anything that encourage core cities, other than perhaps Pingala + Oxford or so but I have not seen anyone employ such strategy. Even in a generous case of 2 science per pop in your Pingala city it is still not that good, a basic library produce atleast 2 science and often more as well as great people Points. And also this is just 1 city rather than several cities.