Mercs don't lose to barely anyone in my experience. I'm a 48 arsenal merc and i hardly ever lose in 1v1. the other day i was on voss about lvl 46 and i was attempting to kill myself to go back to med-station (fast travel was still 15 mins away)
so i agroed 2 silvers and shortly after mako died a 47 trooper came by and thought he'd lend me a hand and started attacking me. I didn't want to give him the satisfaction of my death so i fought back and even with 2 silver mobs on me i still beat him down. then 10 seconds later the mobs finally finished me off and i fell dead in front of his corpse.
before that on voss a consular came by and thought he could take me and i beat his face in, then when he went to rez on the spot i stealth scanned him and killed him again just for good measure.
And before that on hoth i had just hit 40 when a 42 sentinel thought he could take me while i was in combat and i wasted him too...this one was dumb as a rock though, because he kept coming back for more. He came back and attacked me like 4 times each time ending in failure, after i thrashed him so many times he had to bring back 6 lvl 50's from his guild.
anyone who says a merc loses in a 1v1 is doing it wrong.