Earlier quoted context omitted.
Text algorithms (swipe, prediction and autocorrection) create issues on performances of the mobile devices (swiftkey for instance is super slow) and often mistakes due to misunderstanding meaning slowing down the typing experience.
google keyboard is unsuable currently on iOS 11 (iPhone 6S), but that might also be because Apple updares are messing up with older phones.
For my experience working on iOS is very complex for third party keyboards. Also Google has problems with it. :-(