To be fair, he had not enough time. And what he did in his years as Caesar and later as Augustus was almost a wonder.
There are a lot of wonders in roman history.
1. the first major wonder was, that the roman republic made the transition to a monarchy and not ruined itself and the entire mediterrenean world in a very short timeframe
2. the 2nd major wonder was, that this empire based on some very fundamental structural flaws managed to surivive the 3rd century crisis
3. and finally that the roman empire managed to survive the Völkerwanderung and just lost a few (not that important) western provinces.
Well, finally the roman empire went down fighting in 636 AD and became just another medieval kingdom of usual size. Not worth to be called an empire anymore. So finally Fortuna stopped smiling on the romans. Not the fault of the romans. Godesses are sometimes bitches. Simple like that.
A lot of people on this forum are asking always, why the roman empire could ever fall. And they try to rescue the roman empire with reasonable and plausible alternate histories. The right question is, why the hell this political misconstruction led by guys with a very questionable mindset could survive that long!
So no dude. Julian is just one of the many
minor wonders of roman history!