Wouldn't have helped. It's not like doing the first prequel got him in shape for the second, or the experience of the prequel trilogy prepared him to make a quality film out of Red Tails. The truth is that Lucas was never a good director. A lot goes into a finished movie, and several players on the original STAR WARS contributed to the ultimately successful on-screen product. The actors famously complained that his direction on that film was almost nonexistent. The production limitations which were brilliantly navigated by Gary Kurtz, Rick Baker, the VFX department at ILM and others delivered the look and tone we could all believe in - an aesthetic which frustrated Lucas until he was able to "fix" it with the awful Special Editions, or do STAR WARS the way he'd always wanted to with the Phantom Menace. While there were some great hires on the original film, it'd be a mistake to credit Lucas directly with Ben Burtt's iconic sound design or the brilliant production design of Ralph McQuarrie. It's well-documented that the original Lucas-driven cut was a disaster of pacing and structure, before the edit was rescued by Marcia Lucas. To understand Lucas as a director, all we have to do is look at the projects which he had more direct control of top to bottom: THX-1138, the Star Wars prequels, and Red Tails. He's not a good director, and never was. Just a great idea guy and a brilliant businessman. It's not a terrible exaggeration to say that I love the universe established by Star Warsdespite him, not because of him.
Try watching American Graffiti with the audio commentary from some of the actors. You'd be surprised.
They recall Lucas redoing takes just to make it look more spontaneous & natural, encouraging the actors to improvise dialogue & actions . . . it's hard to believe it was the same guy. They describe him doing exactly the kind of stuff that the later-years GL seemed utterly incapable of.
I don't know exactly what changed, when, or why. But the young GL did show directing chops that would have blown the PT out of the water.