There appears to be some speculation about something changing on the iOS keyboard / autocorrect, causing it to get worse in the past few years. You're not alone!
Based on my experience with my iphone, I have a suspicion they've optimised somehow for people having fatter fingers. I've noticed that sometimes the auto correct assumes I mean to press a character next to the one I wanted.
My previous guess was the original version had spaghetti code (ex: lots of hard coding edge cases), and they tried to move it to a more standardized / maintainable code block that hasn't been fully brought up to speed.
The guess was based on a interview video I saw discussing the various prototypes for the original iphone keyboard.
