It's always so interesting to me, the different asynchronies! For DS it was a problem the same way it is for your DS, that they could do more in other areas if not for being perfectly average, or below in this area! But for my DS he could move ahead in reading and science without really being held up by the writing. He could choose to tell his stories out loud or beg someone else to draw something (which we admittedly did too much of). So the fact that K insists on it, and is using something which he is responding to, is a real relief. He seems to understand the process which he wasn't getting before.
Our K is writing most days if not everyday and uses that creative spelling, where they spell the way they think it should be and then learn it correctly later. as it was explained to us, they don't then get held up by freezing over what to do whether its letter formation or size or which letters go together.
Might be worthwhile to find out their method and either add aspects of HWT or get them to. In the meantime, hope the online thing works out, it can be so frustrating when they aren't doing their passion or interest because their hands are too small or some such!
DeHe