A successful U/U/G game will give you enough XP to get a lvl 1 character up to lvl 10/11.
Another one takes you to lvl 14/15. From here it is almost like playing a lvl 20 character.
This "strategy" will increase your N7 rank quite fast and requires at least some skill, if you don't want to leech.
You might even learn something new about the character you are playing.
Playing lvl 1 characters in U/U/G lobbies with 3 randoms is fun. 
Discuss!
This but I like to start at level 6. And do platinum. That really levels you up quick. My take on N7 points:
N7<120 - This person is brand new.
N7>10,000 - Wow, this person has promoted a ton
120<N7<10,000 - Might tell me a little, but less than I'll figure out in the first 3 waves playing with them.
Cool points tell you more, as you can't avoid getting them. Or I guess it is harder to avoid getting them. 120/100,000 is probably a better player than 3,000/3,000.
If you got N7 points for every 1,000,000 or 10,000,000 in XP you accrued, even if your character were level 20, then I would be much more likely to agree with the OP. Or change it to conditional: High N7 probably means high skill. 3k is the bar? Fine. Lower than 3k does not mean unskilled, or have any bearing on skill, because plenty of really good players don't promote.