We all share your frustrations, at least to some degree. I have a son who has many of the same traits as yours. He is also 11, very verbal, chatty, and bright. His handwriting, spelling, and effort do not meet my standards. What I say to you, I say to myself.
Character matters most.
We are called by God to raise Godly children, not scholars. I have learned that a perfect paper is not within my sons capabilies for the most part. He is not a detail guy, one look at his room would tell you that. His thoughts are good. His understanding is good.