The one who made the blurry paintings was the one I started the Centurian challenge with, she had these traits:
Artistic, Ambitious, Handy, Loner and Over Emotional
Then that game became buggy and I restarted with a different sim:
Loner, Over Emotional, Perfectionist, Bookworm, Artistic.
She hasn't made quite as many pictures as the first one yet but she did just max the skill and none of them have been blurry. Here are some:
This second sim is also a writer and she wrote one childrens book. I wonder if that explains the painting on the left.
And the first one often made abstract geometric patterns, the second hasn't done that at all, could that be the handy trait? The perfectionist sim made much better pictures from the start, the first sim started out making stick figures and stuff like kids do in kindergarten.
I think the traits matter a lot and maybe also the activities they do and the places they go. Maybe your sims with boyfriends make romantic pictures?
I want to do more painters, this is interesting.