Why is my voice to text and auto correct getting worse and worse

I used to be a die hard Samsung girl until I received my first IPhone 6s plus as a gift 2 years ago. I instantly fell in love with the phone. But gradually the auto correct and voice prediction has gotten to be more of a pain then it’s worth. It doesn’t know the difference between to, too and two. In fact even when I type it will auto correct to wrong form. I just started my own business and it’s essential that emails and texts come across professional and not like I didn’t pass elementary school grammar class. What is going on. How do I fix it. I am currently using an iphone 8plus. Is it because I have an older model. I had to get a second phone for work, I chose a google pixel. This doesn’t seem to be an issue with that phone and I’m pretty disappointed to say I’m already considering switching back to an android