A couple of points I have.

Lee's strategy, on every day of battle, at Gettysburg was primarily on taking Cemetery Hill not just Culp's Hill.

Ewell could not take Culp's Hill on the first day because Lee really did not have any support available.

Ewell's failure on July 3rd had to do with Pickett's Charge being too late to support Ewell's efforts. Ewell was not the supporting force on this day, Pickett was. The attacks were to be made simultaniously and coordinated to press the Union forces like a nut-cracker early in the morning. Pickett was not ready until much later in the day.

You are correct, the hills on the Union left were not the objective at all. The Confederate forces were all to move towards the focal point, Cemetery Hill. Those Confederate forces on the Confederate right were moving in an oblique left advancement, trying to roll up the Union forces towards the focal point, Cemetery Hill.

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David Upton