When he was the only force user left alive, sure he was the strongest then, but that was kind of by default.
The Force Unleashed games didn't help matters either. As Yahtzee said in his review, it's hard to see Luke as the second coming of the Jedi when all he could do was move a lightsaber by grimacing real hard at it for an hour while Galen Marek is clearing entire hallways full of stormtroopers with a cough. That's one thing I will not be missing from the original EU.