I don't know if this was changed in a patch or something, but I am definitely being awarded limitations badges on "arcs" that are only one mission. I just got the seven badges for the 20-24 bracket in under 15 minutes through the mission Recover the Chameleon Suit. There is a single mission, and you get a Chameleon Suit temp power upon entry that makes the freaks ignore you. You just speed to a glowie, click it, mish and arc over in 2 minutes.
I have been doing the same in the previous brackets as well - just running single mission arcs and raking in badges.