Autocorrect features have some flaws that I have come more and more annoyed over the years writing on mobile small screen devices, especially once it became practically impossible to find any decent devices with physical keys. With the touchscreen keyboard an autocorrect feature has become a necessity. It requires great effort and slows me down formidably if I just try to hit the correct keys.
They get a lot of things right and are a great help in writing. It would be a lot slower, or you would need to tolorate a lot more spelling mistakes. But they definitely aren't without flaws. I have previously written about the problems with recognizing mistakes that I'm more prone to do as a non-native speaker.
Another annoying issue, which I would assume would be easy to fix is mistaps. Having a little bit of logic recognizing the adjacent letters shouldn't be too hard. For some reason it doesn't seem to work all the time. I have noticed some obvious mistakes with no other possible spellings than replacing a single letter with the one next to it, but still, I don't get that suggested. Instead there might be some other words that aren't even close to being such an accidental missclicks.