That is only because Lucas could not acquire the rights to use the Sunrider name. Had they been able to use the name, those story elements would not have been changed to accommodate a new character.
In the end, however, Nomi was an expert with a lighsaber and a master of the Force. She had only been a Jedi for a short while when she severed Ulic Qel-Droma from the Force. There's no telling how powerful she became by the time she was appointed Jedi Grandmaster of the Order.
Because Ulic was deepy in sorrow of Cay's death so he didn't resist.