How is that possible?

I played a game in ranked. I played Meowsacarada and started relatively successful. I wanted to go mid but a mewto and a gengar both did go in the middle (just stupid). When i hit lvl 8 there was a Darkrai lvl 11 coming at me. Ofcourse just killed me without hesitation. The whole game he was like 2 or 3 levels above me(i was the best of my team). I know you can get a higher level with going middle, teamwiping on one side and tgen just farming kills. But he was way to overleveled way to fast? What strats are there? Did he have a teammate with exp-share just helping him level up? Like what is the best strat to get exp? Im playing this game since it came out i think but i have never seen such a big headstart. Please tell me about your thoughts.