Simple does not mean short. I can give you a one line take-home assignment that will take a lifetime to build.
In any case, if it exceeds one or two HOURS, it's too long. And I have never seen a take-home assignment that did not.
(some companies pay for your time for take-home assignments, obviously that changes everything)
I've been at a past company where we (well, mostly I) set up a take-home that would take a mid-level web dev familiar with the material maybe 15-30 minutes to knock out, basically just to test if candidates could produce responsive CSS layouts and knew how to make a proper web form work. It was wild how many we got back that still didn't account for basic (explicitly outlined) use cases like 'works on a phone screen'.