Ewell replaced Jackson after the latter died in May. Ewell failed to follow up his victory of July 1, and then let the Yankees entrench on Cemetery Hill. Jackson NEVER would have made that mistake, and would have taken and secured the high ground.
Had Jackson survived Ewell would still have commanded the new third corps in the Army of Northern Virginia. The reorganization has been planned for some time. Lee thought, quite rightly, that a two corps format led to units too big for one general to maneuver. Jackson's death did not initiate the reorg, and his survival would not have prevented it.
Ewell failed to follow up his victory of July 1, and then let the Yankees entrench on Cemetery Hill. Jackson NEVER would have made that mistake, and would have taken and secured the high ground.
That was Hill more than Ewell. Hill's corps was first in the battle. Ewell came in later in the day and engaged the Union right. Ewell's major failing was not taking Culps Hill on July 1st. And July 2nd. And July 3rd.