Unlikely to be any male currently dominating the mid-distances, because the older greats are way past their prime and hence, their being busted would be less harmful, although they did just bust the women's world record holder in the steeple, along with some major Kenyan women marathoners from the same group as each other.
Kiprop was the best 1500m runner from roughly 2008 to 2015, except for at London. That is a long time to dominate and he ran 3:26.69. One odd thing was that he didn't run any fast times for years until he started to go for them, and got quite a few of them. I don't know if it is him (Kemboi might be more likely), but this is why I was skeptical of including the multiple Kenyan runners who have run faster than Willis in my listing of likely clean world bests at the event.