With 100 functions and one datastructure it is almost as programming with a global variables where new instance is equivalent to a new process. Doesn’t seem like a good rule to follow.
The scope of where that data structure or functions are available is a different concern though, "100 functions + 1 data structure" doesn't require globals or private, it's a separate thing.
One can always look as global variables equivalent to a context object that’s is passed in every function. It’s just a syntactic difference whether one constructs such data structure or uses it implicitly via globals.
What I am getting at is that when one has such gigantic data structure there is no separation of concerns.
Separation of concerns is still a valid paradigm with a single global datastructure like GUI, Microservice, Database and etc. In such situation one can still seperate concerns via composing the global datastructure from a smaller units and define methods with respect to thoose smaller units. In that way one does not need to wonder whether there are some unattended side effects when calling a function that mutates the state.
Seems like one is backpedaling because one was just talking about one's separation of one's concerns and now one is defending one's separation of concerns with respect to one's global data structure.
I still firmly believe that one ctx object and hundred functions/methods is as bad as programming with plain variables defined in the global scope. If the ctx is composed from smaller data structures with whom the functions are defined, then all is good. This is the opposite of the rule.
In languages without generics, like C, people tend to build a custom list type that only holds their particular type. This leads to a proliferation of list types each with sparse feature support.
It is better to have one collection type and use it everywhere directly.
Some Java developers had a tendency to encapsulate collections in <Type>Manager classes that grant limited operations/access to the list type. In practice this doesn't really buy you anything and you could have had a regular List<Type> instead.
"one data structure" doesn not have to mean "all data it one instance". Each of 100 functions could take a slice of data, or use a separate datastore which has the same structure. Separate instances of one structure can be passed by reference or value, and the receiver, because all 100 functions use the same data structure, understands what to do with what it received.