No he isn't.
First of all, he was a young player went from a weaker league to a top league. And secondly, had a lot to learn when he went to Madrid, redcafe spunk at the time notwithstanding. And was often kept out of the side by a more prolific Higuain.
In his last two seasons at Lyon he scored 23 and then 31 in all comp. After a hard first season in Madrid, he scored 26 in his second season and then 32 in his third. So actually, he became more prolific, despite having to share duties with Higuain. That he's since gone off the boil is neither here nor there.