One could argue that it did come at Cassville and that Hood, or fate, botched the whole thing. But then, the buck stops with Johnston, doesn't it?
I do think Hood bears most responsibility for Cassville, but my point about Johnston is that he was the wrong man all along, from before the campaign started.
It is undeniable that Johnston took a battered, disgruntled and disheartend AoT from Bragg (through Hardee) and turned it around, revitalized it, and got it in shape to fight in the Spring. He did that very well. The problem was with everything else he did (or what he did not do).
Someone has to be responsible for the Snake Creek Gap fiasco. Wheeler certainly looks bad -- but Johnston doesn't seem to have done much to find out what the territory was like, to prepare his defense for a flanking move, or to make a defense in depth.
When the AoT pulled back from Rocky Face Ridge, they failed to destroy the RR tunnel (Wheeler was told to do it and didn't). But Johnston had been sitting in place there for at least 2 months: why didn't have a plan in place to take it out?
Johnston seems to have never had a real plan, found fault with other's plans and never wanted to present one of his own. His behavior is the same in Virginia in 1862 as it is in 1864 in Georgia. If a man like George Thomas had been holding the road to Atlanta for the Confederacy, Sherman would have run into prepared positions at every turn; the AoT would have fallen back into a new prepared line every time it dropped back. Unflappable in a crisis and capable of handling it on the fly, Johnston also seemed incapable of being organized and pre-planned.
Johnston's biggest flaw seems to have been that he was always waiting for the perfect moment. He didn't impose his will on the enemy; he waited for them to let him strike a sure stroke. Those moments never came.
Successful generals are not like that. They face uncertainty and the uproar of battle by making events turn their way. They act where Johnston waited. It isn't that simple; you need the talent to carry through to success -- but whatever it is, Johnston didn't have it.
That's why I say Johnston was the wrong man. I don't really think the Confederacy had the man they needed in 1864 (surely not Bragg or Hood which would leave ... Beauregard???)
This accusation is always thrown at Johnston in the context of the Atlanta Campaign. Why? Lee didn't seem to have any master plan to stop Grant, did he? The disparity in forces in both Georgia and Virginia in 1864 was such that both commanders had little choice but to respond to the actions of their opponents.
To begin with, Johnston was much closer in numbers to Sherman than Lee was to Grant.
An attacker needs a surplus of troops in much cases, because he will generally take heavier casualties and his army will bleed troops to detachments to gaurd the LOC as they advance. Grant handled that by shifting his base along the water route as he advanced, leaving himself more or less isolated from Washington at times; Sherman was stuck with a single RR and could not stray more than three days wagon haulage from it, limiting the range of his movements.
Sherman had a harder task in many ways -- yet Johnston let him maneuver the AoT into retreating time after time after time without a serious fight. Grant, with what might be called an easier task, with multiple ways to get at Lee and Richmond, with more resources to deploy, took a year to take Richmond and destroy the ANV. Sherman advanced about the same distance against Johnston/Hood, took Atlanta but blew the opportunity to destroy the AoT at Jonesborough and let them escape.
The difference comes down to Lee and the ANV and the fighting they did. Lee didn't "respond" to what Grant did -- he struck hard and tried to make the initiative his own. He succeeded in the Shenandoah and against Butler. He came close against the AoP, might have succeeded against someone other than Grant/Meade, hammered the AoP at The Wilderness at least as bad as he did Hooker at Chancellorsville. Grant and the AoP stood up to that, took the initiative and fought on -- Lee continued to fight, bled the AoP at every chance until at Cold Harbor another chance was taken away by the ANV and the AoP seemed to be done. Then Grant took one more risk, tried for one more killing stroke -- and Lee blocked him again despite Beauregard's dissembling.
Lee had much more detailed plans for dealing with Grant and was alert and watching when Grant moved, moving instantly. Johnston seems unprepared for anything other than a direct assault on Rocky Face, is surprised by a flanking move, and immediately falls back and is hustled along by Union movements time-after-time. Johnston's retreat is a mish-mash, yielding valuable territory easily, failing to destroy the RR tunnel, etc. Johnston can never find a spot to attack, rarely has a prepared position to fall into, never maneuvers to gain the initiative himself.
Left to himself, Johnston would probably have held Atlanta longer IMHO -- but would have lost it just the same, maneuvered out, probably with an AoT in batter shape. Hood was beyond his depth, seeing opportunity and trying to grab it, but never really doing what would have worked and handicapped by the fractured command mess he had helped create.
What the AoT needed was a credible force to maneuver against Sherman's LOC. That is what Lee was so successful at doing through the Shenandoah in 1862-63-64. It is what Johnston never did. Dividing the AoT into 4 smaller corps is an attempt to get to that, a detachable force of 10,000 or so of all arms under an independent, aggressive commander, and set it loose against Sherman's rear.
That force needs to be big enough to fight off decent-sized Federal attacks. It needs to stop traffic on the RR not for an hour or a day, but for a week or more. It needs to move and strike, dance away before it is crushed. It needs to be a constant threat, so that Sherman has to slow his advance and detach troops to crush that will-of-the-wisp.
I doubt the Rebels have that commander, but they needed him. That's why I mention people like Taylor (in LA) and Forrest (in MS). It is very unlikely they would have been given the post, but they look like the type that is needed. Doing what Johnston did has little chance; doing what Hood did seems to have less.