I'm torn in this one. It's difficult to quantify when a player has graduated to a certain level of experience, as there is a considerable gap in skills that cross a wide spectrum.
But we are still required to assign some level of achievement, some graduation that says, "by now, you should know to whack it before you spray it". (to quote some of our more interesting sayings)
As for understanding the core mechanics of the game, 3 does indeed seem to be the level at which most people get it.
But true mastery doesn't come till much, much later, if the person is willing to put the time and effort into learning the game. By then, your level means nothing, we already know who you are when that person reaches the status of an ace in Icarus.