What is the point of PBE if champions like Vlad and Malz can make it out?

It really makes no sense to me that we have the public beta realm and it serves pretty much no purpose in terms of balancing. Champions and items still come out in a completely broken state. It isn't for lack of feedback that these champions come out in a broken state, often the feedback is completely ignore. I know the sample size is pretty small, as not many people play the PBE, however, it took about 6 hours for Riot to hotfix nerf Malzahar, despite the fact that he was on the PBE for days and in development for weeks. There's either a disconnect between the player testing or the balancing team. In either case, we need to find a better way so champions or items don't come out completely broken and really hurt the health of the game