Too literal. It's the file system syscalls translated into node which are the problem. Anytime you have the potential to block you lose the relatively clean event loop and enter libuv which is a thread provider.

'Lightweight logic layer on top of libuv': well if I can design, predicate and tout my language on 'event' orientation but then when it needs to do something else it becomes a thin logic layer over the hosts threading model: that's just a win!