Joe and his men were the sine qua non of CSA win at Manassas but to say JoeJ did "most of the actual work.." I think overstates Joe's command role and workload prior to the battle. By the end of this battle however it was firmly Joe Johnston's Army until he was WIA at Seven Pines.
Joe Johnston did do most of the actual work at 1st Manassas. His Army may have been smaller but he was the ranking general at the scene and after leaving the preparation staged to Beauregard - who he assumed would know the area better - he found himself stood on Look Out Hill for hours while Beauregard dithered. Beauregard had wanted to attack McDowell at Centreville but McDowell got the drop on him and attacked the Confederate left. Depite hearing the sounds of battle from his position Beauregard did nothing about it. Jackson and Bee's brigades arrived and were directed to the left flank by Johnston who then convinced Beauregard to send Wade Hampton's arriving brigade to the left as well. Finally, after getting fed up with waiting for Beauregard to take command, Johnston declared that the battle was happening on the left and he was going there to take command. Once at the left flank both Johnston and Beauregard rallied the men before Johnston fell back to Portici to form the rear-HQ where he could sort out the battle, find reinforcements and get them forward and send the rest of the arriving Army of the Shenandoah to the battle. It was then when Edmund Kirby Smith arrived that Johnston personally led his brigade to the Federal flank, then sent Early's brigade there as well to launch the flank attack that won the battle. All though this Beauregard had done little but act as a cheerleader on Henry House Hill.