Being fastest doesn't mean anything when there's no mod detection either. At this point it's easy to, for example, decrease car mass by 50kg and increase power and downforce by a couple of percent. You can make changes that are difficult to detect but will have significant performance impact. Until there's proper mod detection and (hopefully) some form of official leaderboard these hotlap times should be considered entertainment and taken with a pinch of salt.
edit: Note that I'm not actually accusing anyone of cheating to get to the top of leaderboards; I'm just saying that at this point it's possible.