I can't help you not one bit. I am eager to learn more about the sanskrit horimono. I was reading that attribution by Horimono is possible, but I am not sure if that is true in all cases, and I am not sure if it would be possible in this case. I have looked at lots of pictures of horimono and this doesnt seem to be the worst one of the lot. It could have been carved when it was made, or when it was reshaped and or at some later time. There is a lot of speculation in this field. I can not comment on if the horimono is low quality or high quality, although I just read that the simple horimono was common to the earlier periods and wasnt as intricate or flashy as they are in the edo period. I am hoping some the big guys here make comment.
In my opinion I would suspect that the horimono was left unfinished and the only thing I see that is truely low qulaity is the photo...
The piece is certainly worthy of better photos.