Are you tapping the keys or swiping over those that make up the word you want to type? In my experience, tapping has always been and remained poor but swiping is getting better and better with every iOS version.
Swiping through keys doesn't have anything to do with autocomplete. Autocomplete has to do with predicting which word you're going to type next, not guessing which word best corresponds to the swipe you just made.
