It was pretty sophisticated. The fact that it was able to make an unmanned flight is an example of something that was superior to the Shuttle. It just didn’t get the resources needed to keep flying, which is a separate issue.
Not to argue that the Buran was "far ahead" of the Space Shuttle, but reasons for not continuing to use the Buran include many others beyond it not being advanced enough. Whether or not it was useful or economical to continue using it are also legitimate (and probably more likely) reasons for it to have been discontinued regardless of its technological achievements. One could imagine the Soviet Union wanting to continue flights even if it weren't more advanced if it were otherwise reasonable to do so. (And that also ignores internal politics.)
