The only word that comes to my mind, is being literate, but that is just a person that can write altogether.
Is there something for people that can write in a "better" way; someone that just writes "fancier"?
For "Mr. Dave writes really good sentences" would you just say "Mr. Dave is literate in English" or is there a word that would fit in "Mr. Dave is ~insert word here~"?
I know that "writing good sentences" is kind of subjective but I hope I could bring my point across.
He can write *more articulate* sentences
, right?