I doubt that it's possible to give a clear definition of what makes a translation good. I've heard that there are better works than Kumarajiva's, however, since his have the prestige and sounds good in Chinese other translations are not used that often. It is the natural selection of translations. Which means that it's better to have more than less, and what is good for one can be bad for another. For a translation to become the definitive version requires either central force (like in Tibet and Theravada countries), or just trends that can change in different eras (like in East Asia).
"While teachers of the middle way, mind only, transcendent wisdom, mantra, and other schools may have their own assertions, the fulfillment of those intentions is the same. There is not a single thing that is not contained within mind."
(Gampopa to Düsum Khyenpa, in "The First Karmapa", KTD Pub, p254)
“If you recognize the world of appearance and existence as the mind, realize the mind itself as empty, and have no grasping at the superiority of your realizations — this is the ultimate view."
(Chegom Dzongpa, in "The Book of Kadam", Wisdom Pub, p609)