Exactly!
Load a 4GB file and welcome the beach ball spinner any time you need to context switch to another app.
I don't know how they don't realize that because it's not really hard to get there.
But when I was enamored with Apple stuff in my formative years, I would gladly ignore that or brush it off so I can see where they come from, I guess.
Isn't that exactly the upthread contention: Apple's magic compressed swap management is still swap management that replaces O(1) fast(-ish) DRAM access with thousands+ cycle page decompression operations. It may be faster than storage, but it's still extremely slow relative to a DRAM fetch. And once your working set gets beyond your available RAM you start thrashing just like VAXen did on 4BSD.