Am I understanding this right? Republicans passed a bill that Trump considered very important, but they did it only because someone on the team did some pretty unethical stuff (not highlighting changes in the Bill draft) ?

We shouldnt be doing stuff like this. Imagine you are negotiating an important contract (say buying a home, or a employment contract, etc) and the opposing team sends you an updated contact supposedly highlighting the changes, but intentionally does not highlight some crucial changes that has adverse effect on you, and you end up signing it. You wouldn't like that and its highly unethical if not illegal.