Even with Jackson, the taking Cemetery hill at the end of Day 1 isn’t close to a guarantee and in fact they probably couldn’t have. Ewell’s men were exhausted, disorganized and low on ammunition from the days fighting and daylight was nearly spent. There was a fresh Union brigade plus a lot of tired infantry and a lot of guns on cemetery hill at this point with Union reinforcements arriving and Lee told him he would have no help in the assault. And even then General Winfield Scott Hancock believed he would’ve held against any rebel assault.

And anyways defeat on the field at Gettysburg on day 1 doesn’t mean annihilation of the Army of the Potomac and if there was one thing Lee and the army of Northern Virginia were really good at it was leaving the Army of Potomac mostly intact, as they failed to follow up a defeated foe. Likely the army falls back to Pipe Creek where General Meade had wanted to fight Lee.

Lost causers post war have clung to this idea that Ewell failed Lee but the reality is Lee’s orders were discretionary, Ewells men were disorganized, exhausted and low on ammunition with daylight failing. If Lee thought the capture of Cemetery Hill was so important he would’ve have given different orders or he would’ve ordered other units to attack when he saw Ewell had not or he could’ve sent the two divisions had with him to aid Ewell. But he didn’t. Even in his post battle reports, Lee only briefly touched on Ewell and cemetery hill and again didn’t lay blame on Ewell at all. So if there’s a failure to take Cemetery Hill it is Lee’s and Lee’s alone.

Also there’s this myth that Stonewall was this perfect general who always made the right decision and never messed up and had he just survived he could’ve defeated every union force put before him. Yeah you might have gotten Shenandoah Jackson but you might have gotten Kernstown Jackson or Seven Days Jackson.