An example of the blacklist job:
On 20 October 2016 we stopped 35916 requests.

Here are listed the 100 ip more present in the block log:

https://public.etherpad-mozilla.org/p/XV1d8eHFTY

Feel free to check these ip against http://www.stopforumspam.com/search

and evaluate the statistical possibility to match username/email - ip and what those ip are doing during the last months.

I hope this could explain why tor is only the smallest part of the problem.