Being both a guitar player and a bass player, I certainly wouldn't say bass is easier. I would say to be mediocre at either is pretty easy. To be a good bass player is probably harder than being a good guitarist if for no other reason than once you learn a boatload of chords it is merely rote memorization. Bass lines are often much more detailed.
I can tell you that it is much easier to sing while playing guitar than it is to sing while playing bass. And in any respect, wanking away on 4 chords is much easier than repetitively walking the same bass scale, in time.