And there is like no way to track it - no kill camera or replay to watch if the kills were legal or not.
Then how can you say they're aimbotting ? If there's no proof to say they're not cheating, there isn't either one to say they are.
Obviously not everyone is clear, but often it might just be an impression caused by lag, Paladins' hitboxes or the general paranoia caused by the lack of a way to verify it, as you stated.
Because when someone aims you as a sniper behind 2-3 walls and always does a headshot is something.