I suspect they're referring to graphs of Drop implementors, based on the sibling thread. If you for some reason have a linked-sea-of-nodes data structure that has to traverse itself on drop, that can behave similarly to dropping an Rc graph, though it still doesn't use lifetimes.

I guess that would make sense, but I'm not sure it's lifetime-specific though. C++ doesn't have lifetimes but would still have this problem.

Yes, C/C++ would also have this problem. The point I was trying to make is that incrementality/latency is a property of a runtime. If your program has deep ownership graphs, any kind of naive reclamation procedure is going to have high latency, even if it's written in C/C++.

Quite fair! Thanks for elaborating.