Ewell offered to attempt an attack if Hill would support him but Lee told Ewell that he would be on his own. Ewell was left to make the call.I do not think that Ewell alone could've taken Cemetery Hill on the 1st of July. A joint attack from both his and Hill's corps would make more sense, but organizing it was a little above his pay grade. I may be wrong, but I think that General Lee himself was at that moment at the positions of 3rd corps and made no attempt to organize an attack on Cemetery Hill. Can we blame Ewell for not trying if Lee himself didn't try?
Ewell also recognized the importance of Culp Hill and gave Edward Johnson orders to attack it. Johnson, when he got there, incorrectly appraised the number of federal forces on the Culp Hill and didn't attack. Here we can scorn Ewell for failure to give more precise and deliberate orders to Johnson.
I agree what Ewell's performance on 1st of July was much better than it is usually painted. The problems of AoNV in Pennsylvania Campaign were a little above Ewell and came from the recent major reorganization. Some time was needed to make all officers and commanders (not excluding Gen. Lee) to accustom themselves to the new structure.