Of course for a monthly chart where you take into account stats prior to the 4th of july you'll have this kind of curve, as most of the new users came from the month of july... What happen before 4th of july is what i would call a pre-launch. So it should not be taken into account.
And as right now we are in august, having a monthly chart where only july count, doesn't provide any sufficient data imho to conclude that Steemit has reached escape velocity.
For me when on the account creation per day chart (https://steemle.com/charts.php) the curve will go up to the north then it will be trully viral (not counting once again DAUs or retention rate)