Shang Tsung can steal souls and shapeshift, good for him. But he did not make himself younger that was Shao Kahn (read the MKII comic book) and the only reason he steals souls is because of a curse and it's necessary to sustain his life - it's a weakness not a strength. Quan Chi opened a portal to the Heavens so Tsung wouldn't be a vertiable junkie vampire and could retain some dignity. Quan Chi can travel the realms undetected by the Elder gods (as per MKM: SZ), something that if Tsung could do, Kahn would have taken Earthrealm years ago. Also Quan Chi had the balls to steal the Amulet from Shinnok and the ability to keep it hidden from him during the events of MKM: SZ, MKI, MKII, MK3 and MK4 where he used it to destroy the fallen Elder god. Don't forget Tsung was altogether 3 times unsuccessful in taking Earthrealm. The only way Kahn was able to finally invade was by resurrecting Sindel and that was only possible, in the end, because of Quan Chi (MKM: SZ). As for his ability as a sorcerer Quan Chi's fighting prowess (which was enough to kick Tsung's ass in MKD) comes solely from his deep understanding of sorcery (MKDA Konquest). Not to mention the words that came directly from John Vogel's mouth, "Quan Chi is the oldest and most powerful sorcerer." I rest my case.
I couldn't agree more that MKA''s story wass an atrocity. I know it's taboo to say, but MK9's story is shaping up to be even worse IMO. Don't forget that before Quan Chi had the Amulet he freed Shinnok from the Prison of Souls and helped him defeat Lucifer after a centuries-long war. That has to count for something.
It said is his MKA bio (which you'll have to find online):
Long ago I had pledged my soul to the emperor. That pledge was binding even beyond death. But if he were to die, so too would those who served him. At the time I believed it to be merely another empty vow, yet here I am. My soul has returned from beyond to rejoin Shao Kahn.
As for Quan Chi's sorcery, see my other post(s).
He wooped ass for (presumably) 9 straight Mortal Kombats until the Great Kung Lao arrived. Since then, about 500 years, he's been getting his ass whooped in some form or fashion by pretty much everybody he fights. Personality? Really? Wtf does that have to do with... anything?