Mendes actually has the best blast double in the UFC since GSP and actually shoots regardless of fence or no fence. Mendes leaves more openings to escape whilst Khabib offers options of escape so he could get to a better position.
Khabib has the better chain wrestling and more relentless pressure. He also some of the best GnP in the sport. Khabib is a different level grappler to Mendes.
Khabib poses more problems for Conor theoretically, but Mendes had success because of Conor's knee injury.
Conor either sleeps Khabib or is finished savagely on the ground. I also think Conor has some of the best anti wrestling strategies in the ufc with the framing and cross arm tactics fused with distance control. Khabib also moves back in straight lies with his neck far behind his body exposing his body to Conor teeps and body blows. On the feet Conor is overwhelmingly the favorite, but then again on the ground its Khabib who is just as overwhelming.