Overpower gives MRD a bit of an edge over GLA, enough of one that if you get lucky/unlucky with parties a couple of times, the difference can seem pretty large.

In this case, the DRG would've had access to his combo finisher (Full Thrust), while you were two levels shy of having RoH. Couple that with the differences in gear and yeah, it would've been rough if he just started going full tilt.

Everything tocsin said. I'd also say upgrade all your gear as much as you can (e.g., it's time for Brass Rings), consider putting some (or all) of your bonus points in STR while you're leveling, and hang on until RoH. RoH makes a large difference.