According to Khabib Leandro and DC were the biggest influences on his ground game at AKA. I know he said Leandro really helped him improve his submissions.
Prior to his last two fights against Gaethje and poirier, Khabib submissions were not the greatest. I mean, he used to need to beat guys up for 4 or 5 rounds before being able to seal the deal and most times even then, go to judges.