Can you, for example, spell out what you mean by "you really want your data model to be acyclic and not require GC"? What is cyclic about the "data model" in e.g. Go or Lua?
I can field that one. If a has A reference to B and B has a reference to C and C has a reference to A, then we have q cycle. Cycles play merry hell with garbage collectors and reference count destructors. Languages that force references to be a strict tree or DAG get cheap destruction in return - see C++ without pointers for example - I pop a local object off the stack and it's gone, along with all its children - no non-deterministic GC pause or delay, no Pythonic cycle check. Rust is built somewhat on this principle.
Right. The way I'd put it is: in system software, the iron law is that you don't make the programmer pay for anything she doesn't need to buy.
What you pay (GC) for the privilege of having pointer cycles in your data is grossly disproportionate to the benefit. Yes, there are a lot of things that are O(k) with pointer cycles and O(log n) without them. If what you buy from this optimization is worth the cost of GC, you are doing a lot of these things... a lot.
So "you really want your data model to be acyclic" means, "you want your programming language to forbid construction of cyclic data structures"? So, for example, connected graphs are not objects you can represent?
They do - but arguably being forced to define the distinction between direct hierarchical references, and symbolic links, helps constrain your data model and make it more rigorous.
Note that relational databases don't have back pointers either. All references between tables are symbolic. Last century, people tried to make databases that were general pointer graphs (google "network database" or "object database") - broadly speaking, it was a disaster.