Not an expert on this but from what google says they are detecting and automatically discounting negative seo. I suspect that is due to complaints about the time spent disavowing and inability to practically disavow thousands of links. The problem is that you'll probably suffer until what triggers the automatic discounting of negative links. You can disavow but that is going to be a lot of time spent. Might be more valuable to spend time trying to build/improve alternate sources of traffic.

