User blog comment:ElectricEnder222/Volume 2 Episode 4 Discussion/@comment-4834824-20140815021551/@comment-3146930-20140818014455

Just to point out a few things, we don't know how skilled Roman is with a mech suit. He seemed skilled enough to pilot it, but he probably wasn't trained to use it as an actual paid pilot would be. RWBY on the other hand are being trained to take down larger enemies so they would have a clear edge over Roman in that fight.

As far as Ruby taking down an entire team, this is only partially true. Jaune and Ren were on the floor right up until Ruby flew past them. Nora had also done most of the fighting, taking out Yang and Weiss so she may have been tired while Pyrrha had just used her Semblance on a very large scale to take down Blake, meaning she too may have been tired. Meanwhile Ruby for the most part hadn't done much fighting and was at full power and because her power is speed, the others may not have had enough time to react.

However considering they were all laughing after the fight, no one was really "defeated" and if they wanted to, they could have a real fight.