It really does have me puzzled, I am no where near their skill level but to consistently hit 45+ on a solo player there are some factors that I cannot get my head around.
If in a lobby with 2 or 3 in your party and your up against noobs then fair play, that target may be attainable consistently but from my experience, after each game the majority leave if they get owned.
As its clan ops there is the chance that you get put up against another clan that may be equally skilled therefore being a much harder game and the 45+ on a slayer being impossible to reach.
Host migration, this occurs nearly every 1 in 5 games when I play and about 25% of the time the host migration kills the connection therefore reducing the effectivness of killing speed.
Playing consistently well, from my experience I can top the leaderboards for about 4 - 5 games in a row then I have one terrible game (normally another member in my clan then gets the majority of the kills)
lag, I cannot escape this, surely its the same for everyone else, some games you just can't kill people due to their being delays on your side.
Finding players, I am in the UK so on the Europe servers, if they are in the US i can understand there being more players to find but it still takes time to fill the lobby with fresh players.
Party players being dropped, in game and after game. this takes time to resolve.