Actually, I think that every class *is* meant to score high.
The problem with this is that not every class is meant to get the kills - that is, to finish the enemies.
Sure, every class is pretty much capable of doing well and handing out pain even on the highest difficulty settings. Having said that, its pretty clear that there is supposed to be a sort of division of labor.
For example, maybe one player focuses on debuffs, one on crowd control, one on enemy suppression, and one on raw damage output; this is just one of many configurations, and it certainly isn't meant to be iron-clad even during the match in question. In any case, this is the intention that the power mechanics seem to clearly convey.
The problem is the scoring system itself. Yes, I know, it's a co-op game, everyone gets the same xp, etc. etc. And while I actually agree with this sentiment, it's still a condescending and overly simplistic dismissal of a legitimate grievance.
See, while everything else in the game encourages co-operative play, the scoring system *discourages* it. I can see why they would want a scoring system, and I think that it is a good idea:
1) It's a way to encourage friendly competition.
2) It's a way to satisfy some of the competitive nature inherent to all players to varying degrees.
3) Most importantly, it allows the the designers to reward and encourage desirable actions and behaviors, like reviving team mates, completing objectives, and assisting in kills.
Even if you aren't a hyper-competitive jerk, you still want to feel like you are contributing and get rewarded for said contributions. That can be hard when you score several thousand points behind your teammates because you were the sucker who didn't go with the optimized high dps build in favor of a support class, or even a class you just happen to like.
It's counter-productive to have a co-op game reward the players who finish off the most enemies over those who make equal, if not greater, contributions to the team in other important ways. It doesn't matter if that reward has no actual impact in the game - your rewards, experience, even your rank are completely independent of how high your score was in any of your matches.
But its still a reward, and you don't get nearly as many points for assisting as you do for killing. To make matters worse, of the 13 non-group medals that one can earn during a match, only 2 aren't kill related: revives and assists. And the threshold for assists is so low that it almost seems like a condescending consolation prize.
I understand that Bioware probably didn't consider that even non-consequential rewards could shape player motivation and behavior. But it seems quite clear that they do, and that we should be advocating for a more robust and even-handed scoring system rather than "totally great ideas for balance changes that'll "fix" everything!"