Heth's afternoon attack that cleared Union I Corps troop off McPherson Ridge and across the run- Pettigrew and Brockenbrough, had Archer's battered brigade as right flank support. They guarded the flank from Gamble's cavalry but appear to have not done much to even do that.
There's definitely an argument to be made that the Fairfield road flank was horribly mismanaged and under-utilized by the Confederates. They could have easily extended their line farther south, they had a road on Herr ridge to do so. A problem was that they had very poor reconnaissance and already knew one Union brigade (Biddle's) had popped up on their flank in the morning. Would there be more? If I remember right they also had a battery to protect.
Even just Lane's brigade pushing on aggressively could/would have ensured a worse disaster for the Union July 1st. It's really remarkable when you think about it. The presence of the cavalry was invaluable for the 1st Corps. Archer and Davis' brigade both played a minor role in the afternoon fighting, with some of Davis' guys helping to capture some colors from Stone's brigade. Davis' brigade was surely the body of troops which Daniel (Rodes' division) appealed to for help attacking Stone's brigade near the RR Cut but they didn't help. There's a logical reason for this.
The thing about men that see combat is that they need rest to be fully effective between engagements. It's an understudied aspect of warfare and especially among students of warfare. You're just not going to be nearly as effective when you already dealt with a major shock to your nervous system like that, and it is a physical shock. It was surely a disadvantage to the Union 1st Corps brigades who had already been engaged and one Confederate Lieutenant felt that the effect of combat - wait -
combat was why wounded were howling and foaming at the mouth. Cutler's brigade surely had it much worse than Meredith's.
Throwing units into combat more than once with an extended pause in between is like taking a starting pitcher in baseball and having them pitch before they're recovered. Sure, they can do it, but it's never going to give optimal results. So nobody does it, they'll put a non-pitcher on the mound and consider their resting pitchers untouchable. Maybe not the best analogy vs combat but combat is worse on the body.
This need of rest is almost a central theme in Dave Grossman's book, "On Combat" which way too few war history buffs read IMO. They make pretty much every officer candidate read it nowadays. It's not a perfect book but its the best treatment on the psychology of combat and a huge area of study is the tremendous strain it is on the human body and how it needs time to recover from this. Combat is so terrifying to most individuals (besides
psychopaths) that parts of their brain are liable to begin shutting down. That's why soldiers forget steps loading their musket and keep doing it over and over. It isn't any less complicated than that.
I'll post this mumbo jumbo from part of "On Combat" which summarizes the situation which was surely infecting Archer's surviving men and might answer your question:
Of course in later wars with never-ending frontlines, soldiers often
did not get proper recovery due to the continuous state of combat, alien to their ancestors. Hence the massive numbers of psychological casualties (requiring medical evacuation) which is also often ignored by war buffs, but were huge in number, and depleted frontline units or made them very ineffective if they didn't evacuate these broken guys.
I don't know what would happen if you took Davis' and (Archer)'s brigade and tried spearheading the afternoon attack with them. I'm guessing it would be very poor results for complicated reasons like the above ones. Soldiers can be pushed to their limits in necessity but the grumbling would be severe if asked to do it when fresh troops are available, and the effort would be less-than-stellar.
Pettigrew's 52nd NC had swung right thru the Herbst Farm, and Archer failed to cover their flank and I seem to remember they formed a square in response to the 8th Illinois!
I'm in the minority but I tend to believe the 52nd NC did not
literally form a square but made some other precautions which were later misinterpreted as a Napoleonic square. The idea of cavalry troopers closing with an infantry regiment in that situation is silly. Cavalry is almost treated mythically in their last decades of existence. A skirmish line can't stop a line of battle but it can probably stop a cavalry charge. The wording of some of the language surrounding that makes me think that it was a short feint to force the 52nd to pause as they were routing the 121st PA. That, and the cavalry presence all around, definitely helped and definitely drew Confederates away but did not necessarily leave Confederates shaking from fright but annoyed and having to account for the threat.
Bringing the