The complications rate for measles is about 30% (according to CDC), but not all of those require hospitalisation, and only a very small proportion lead to permanent damage.
That's 70% who are absolutely fine (to reassure anyone who may have a DC with measles or suspected measles). But the inescapable fact is that you cannot tell where in the 70/30 your poorly child might be. Or if, within the 30, how serious is can get.
Complications of the vaccine are far far lower - even allowing for under reporting of side-effects.