Try turning off autocorrect. It seems like a non-option, but I found it made my mobile typing skill greatly improve over the following months, to the point I’m now just as fast while also fully removing that frustration from my life, and also not reliant on a particular phone. Retrospectively, it makes sense: autocorrect numbs feedback, removing the mechanism by which we learn to subconsciously and quickly do what works and avoid what doesn’t.