I think most of the Genins have already proven themselves worthy of being a Genin in terms of skills and powers, for eg. Neji who has been called the Genius of the Hyuga clan and Rock Lee who's able to open 5 of the 8 gates. But although their powers have surpassed those of a regular Chunin, most of them failed the Chunin exams except for Shikamaru, who although was defeated managed to get promoted due to his talent in tactics and planning.

Thus, it is safe to assume that promotions do not come based on only skill and power factor.
Eg. Back in the Chunin exams, if Naruto were to go against a Chunin, maybe Iruka, who do u think will win?

Question then: Do all ninjas need to clear the exams before he can be promoted to the next rank? Or do they get automatic promotions based on powers/seniority/other attributes?
Its not about their level of power... Its all about the teamwork.

However, I think the whole scope of the story has stepped away from the rank of them, since ranks are only determined by what missions you are chosen for, and probaby works in terms of the pay structure. However, Kakashi, Sakura and Naruto are now their own 3 man team. Kakashi is probably team leader, but the fact they're a team, and Kakashi isn't a babysitter anymore is a good sign of their acknowledgement of power.

Though the point of the whole bell capturing exercise again was to see if Naruto and Sakura could work together as a team (original purpose of that test). I think Kakashi did that to see if they would be able to function as a team, and not just be independantly strong, if that makes any sense.

Ultimately, they still didn't really prove teamwork, they displayed individual strength.... again... Though the tactics used to lower Kakashi's guard was effective, and pretty damn funny, how was that representative of teamwork (aside from the discussion to arrive at that solution =P). In that respect, the episode didn't really show how much they've grown, we just kind of assume alot of individual growth.

Long story short, its all about their teamwork.