Are you sure about that? If you have an exclamation point on your time that means it is invalidated, but you should still be on the leaderboard. It's hard to get a clean lap time in single player races because drafting whether you're the lead or following car is one of the things that invalidates lap times.
Yes, I am sure that you are a certified genius. As for the leaderboards I have the exclamation triangle in my lap times (and so do the drivetars) but I am never in the leaderboards. I have tried with dozens of cars on several tracks and with Friction on and off. No difference, unfortunately. There has to be something I'm missing...