[Mike Darancette]

I don't see what he could have done to make the tactical situation any worse for Chamberlain.

Jackson would have probably noticed that taking Big Round Top not only flanked Little Round Top but the whole Union Army. Stonewall wouldn't have needed Stuart to see that.

Taking Big Round Top would have unhinged the right and center of the Union line.

[thescourged1]

When I visited the Gettysburg battlefield, I took a long and hard look at both the Round Tops. Little RT had a panoramic view of the entire area and was a critical point, to be sure. Big RT I don't perceive as being any better than LRT for the same purpose, plus it's heavily wooded thus getting any significant artillery up there was out of the question. LRT would have blocked the line of sight of BRT to the rest of the Union line, in any case.

[Non-Sequitur]

Jackson would have probably noticed that taking Big Round Top not only flanked Little Round Top but the whole Union Army.

Lee made the decision on where to attack. You're assuming that Jackson would have had better luck changing Lee's mind that Longstreet did.