The whole law suit thing is ludicrous. Parallel thinking happens, I'm not a song writer but I do write fiction and have had people say "oh that's like what happened in "blah blah" by "blah blah" which I have never read or even heard of.
I tend to think that if you need to sue people over "derivatives" to make a living you need to take a good look at your self.
I had an American film company rip off on eof my characters, it was obvious, it was too precise to be coincidence ( a 1/2 Japanese female zombie killer named Cas ) their filmed sucked, if they had bought my entire story it would have kicked arse LOL. Did I sue? No. I just felt sorry that they were so bad at their craft they had to steal.