As far as I can tell, efforts to neutralize spam/blatant abuse are led by a small number of people.
They may be (though some of this is probably the larger efforts being more visible) but by far the biggest improvement was simply the switch to RC which cut spam by some very significant percentage overnight (my guess would be 80%-ish).
This could be an example of solving a problem with an arguably more complex system, but one which was well thought out and had broad application (unlike many of the tweaks which were more reactive and impulsively made in the past, but had the effect of layering on unstructured complexity in a more harmful way).
Anyway, I do think we should assess the effects of HF21 which at this point we can only make rough estimates ranging from very limited to profound across the platform.