I hate handwriting with a passion. I have my whole life. I have horrible handwriting and my hand gets sore 5 seconds after I start writing.
I am sure it is because I don't hold my pen/pencil correctly, but I think after 43 years I am not going to suddenly fix that.
I am similar. If I physically write a couple times a week, my hand adapts though. It's a skill like any other.
Fountain pens are nice too since you don't need any pressure.
My writing looks a lot better if I just force myself to slow down and be deliberate, but honestly it's a constant battle. I'd definitely benefit from practicing penmanship on it's own.
You sound likely to have dysgraphia, based on the fact I have all the same aspects and a dysgraphia diagnosis.