That’s why I qualified to to be across the team (team average). In most cases, you have 3 killers and 3 non-killers (typical 2dps and 1 offensive tank, with two supports and 1 defensive tank, for instance). The killers should hit roughly a ratio of 2:1 in that configuration.
Hitting higher KD ratios should be much more difficult unless the match is wholly mismatched (unless you’re counting eliminations instead of kills, which is overall a useless statistic).