I'd say that dramatic score differences do matter to some extent, but helping with objectives, reviving, and really just trying are more important. I just played a gold game where I got over 200K with gold kills, biotic kills, pistol kills, and revive medals, and the others where all 60K or less with at best one silver medal each. I didn't beat them to spawns, I didn't spam missiles, or do anything else that would have given me points without giving the others a chance, I just killed things alongside the rest of the team. That tells me that, well, they sucked, and probably shouldn't be on gold (at least with the kits they where using). Yes, their weapons/mods/etc weren't great, but they should have been able to score more than that, even with considerable lag.
That said, I would be reluctant to base someone's skill off of their score in a single match. They may be trying out a new build that just didn't work, or had bad lag, or just a weirdly bad game. Personally, I have been dramatically outscored sometimes, even when using my best kits. But it is not often, and is usually because someone (usually a BSNer) is just so damn good that I didn't get a chance to kill anything. If you regularly score poorly, you are probably being carried, and should drop down a level to gain some skill/better equipment.
Generally if I don't hit at least 80-120K on gold (depending on the kit) I feel I did unusually poorly, simply because I know that I am capable of doing far better.