I have the same exact situation happened to me about a few months back. My competitor had his site hacked and was having hundreds of thousands of shitty links with anchors like "tom shoes".
He took #2 position from #10 since the spam started. It does help in the short term. But now (5 months later), the link building has stopped about 3 months ago and he is slowly dropping in ranking.
Not like a drastic drop but slowly dropping. To be honest all this talk about GSA being dangerous to the site and all. I have not seen a single case study where a site got penalized cause of thousands of shitty links.
On the contrary, the shitty links seem to help in ranking for the short term (months).