"For me, it seemed more believable that he was spoiled rotten rather than abused."

Which is deliciously hilarious when you consider that Jace is blatantly ripped-off from Clare's version of Malfoy, who countless people have tried to write as being an abused teddy bear and who is clearly shown in canon to just be a spoiled brat.

I think it's more accurate to say that Jace is what Clare thinks an abused kid acts like. Probably her idea was that Jace spent years being hurt and belittled by his father, so he was thrilled to find that being a great Demon hunter with a snarky wisecracker personality got him a lot of positive attention.