Well, considering that, as I said, the top three players (now top four) all have Kill Assist - Medic as either their first or second most common form of point gain, I think the number of points assigned to it would definitely affect people that play the class are ranked.

That's not the case at all. I'm not arguing that killing others is more important than healing (in fact, in terms of a single player's value, a medic is almost certainly more valuable, so a bonus to Kill Assist - Medic seems appropriate), only that the reward for being a medic is currently higher than their true value to the team.

It won't encourage the vast majority of players. It will only make players at the top, who pay attention to the rankings, lean heavily towards medic (where they can maximize their return), and you'll see the top tier filled with them (as it is now).

You are correct that different maps and different circumstances favor one class or another, but the game is pretty well designed, and there's no class that is universally more or less useful all the time. That means, between classes the difference is moot, so you'd expect a perfectly designed point system to never consistently reward one class or another. The problem with the current setup is that yes, as evidenced by the disparity of rewards from only a week or two, medics are the only way to go for someone wanting to get maximum points.

You'll never have a system where every class advances at the same rate, but that's because you'll never have two players of identical skill and circumstances. The system should reward individual skill and teamwork (and part of that entails playing the class the team needs. If they need a medic something fierce, the system should reward the person who fills the role because he'll carry the heavy to victory. But if they need a pyro and already have 3 medics, it shouldn't still reward medics more). If instead it encourages players to choose one class solely because they need the points, the system has become counterproductive in the extreme.

And if my concern were my own ranking, you'd be absolutely right. But if heavies or spies received more points overall than another class, I'd be arguing to reduce their gain just the same.

On a side note, the last few hours I have been playing a medic, both for the incentive it has, as well as to see if my argument really held water. And it does, to an insane degree. The points awarded as a medic dwarf what I would get on any other class. In less than 3 hours I'm approaching close to a 1,200 point gain. No other class holds a candle to that (and I'm not even a great medic). So change it if you like, or don't, but I have no doubt now that as players realize this advantage, you'll see the top ranks comprised almost solely of them.

Edit: Note my current rank after those THREE HOURS is now 3, not 5.