Not quite sure where the 4 pts and 2 assists is written down, but here are the numbers:
In ACB: 5.3/3.3/4.4
In Euroleague: 6.5/3.2/3.5
He is doing it in around 23 minutes per game.
Now, those numbers don't look impressive to most people, but we have to keep in mind that in Europe the pace is slower. Teams have around 70 possession per 40 minutes, that is like 84 possessions in the NBA, that is slower than the slowest team in the NBA. Regal Barcelona had around 66 possession per 40 minutes. If we adjust Rubio's numbers to 36 minutes and the average pace of 92.3 possessions we are getting:
Euroleague: 12.3/6.1/6.6 (with 3.0 steals per 36 minutes)
Those numbers are very much alike the numbers of a younger Rajon Rondo. When Rondo was 22 in 2008 he had 12.7/5.0/6.1 with 2 steals per 36 minutes. And Rubio is still 1.5 year younger than Rondo at this time.
Additional to that Rubio posted a +2.9 per 100 possessions RAPM in the Euroleague, that is 11th best. Rondo had +1.1 per 100 possessions in 2008. So, Rubio's +/- stats showing him as someone who clearly has a positive impact on the game.
So, that's what we likely can expect Rubio to be. A Rondo from 2008 with better passing and free throw shooting.
P.S. In Europe assists aren't that easily to get as in the NBA. In the NBA an assist is also handed out when the receiving player makes a move, that is not going to happen in Europe. The defense on the perimeter is also tougher due to the shorter 3pt line. Rubio is shooting the ball better than Rondo which can be seen at his free throw numbers, but his field goal percentage is lower due to the fact that he has to take much more contested jump shots on the perimeter in comparison to close shots. It is a different kind of game, thus the stats will always look not that great to NBA fans.
There are many discussions about Rubio on realgm and the attack of the stats came up. This was a good response that I have not seen laid out. (Props to mysticbb)