I think it should suffice to know that after one repeatedly trains the google spam filter with "report not spam" and "mark as spam", it should learn that well enough, no?
As an example: Some dumb ass Verizon customer gave them my email address as their own. I got a ton of communications from Verizon that I could not turn off (bill past due, thank you for you promise to pay, and all sorts of really annoying messages). I called Verizon, I was told that neither them nor I could do anything about it because I did not own the Verizon account, and I did not have the account PIN. Their official solution for this problem: Mark all the Verizon emails as spam and don't call them again (I kid you not).
The result: I marked about 100 Verizon emails as spam and Gmail learned that really well; now I do not see Verizon emails in my inbox. Why TF can't gmail do this with all the other emails I mark as spam and not spam?
I just got in the habit of firing up the hideous gmail app on my phone to go through my spam folder every day and vet out the non-spam out of there. I usually go though about 250 emails per day. I end up looking at all the spam, but it's far faster to fish out the good messages from spam than if I turned spam detection off altogether.
No matter how complex the problem to solve is, Google is failing at a level where even I could program it better, which is not a high bar at all.