I don't get this

That's mostly because Rengar is a less safe than Shaco, and because, unless you're next to a bush, you get the chance to know Rengar is coming, while you do not normally get the chance to know Shaco is.

Shaco’s q is an ability that makes him invisible, Rengar’s passive is just basically an enhanced AA that lets you jump to the target. And Rengar’s ult lets you do the same thing as Shaco’s q but you get the leap rang for your AA.