On my system there are 240 tasks running with ~1700 threads. Htop is using 6% of single core with cgroup column disabled and 9% with it enabled. It spends most of the time in kernel space so it's not htops fault.

> While I agree that it is _less_ efficient than some other ways, in what way is that _significant_?

This gets noticeable when every connected user/session runs the htop.