Another part is that Lee lost a war that was materially unbalanced against him, much like Germany in WW1 and WW2 and why you find a similar cope in interwar Germany and by wehreboos about WW2 Germany. Fact is, while they definitely had material disadvantage, their generals were also just bad.
Its easy for people to cope if the winning side also had more manpower, better weapons, better logistics, and communication (union had far more factories, more people, more rail networks, and a complete telegram network back to the White House. the losers did not).
But in my opinion, that is nothing but cope. A good general should realize that they have no chance to achieve victory and instead seek an alternative route, either through diplomacy or an insurgency, not draw out the inevitable and waste lives for nothing.
Related: The Civil War is extremely formative to the US approach to war in a way that went away from the European established approach (decisive battles convincing one side to give up). The US model was broadly "deny all alternatives to surrender", a model developed by the Sherman/Grant "total war".
Lee carelessly losing the one resource he couldn't afford to lose—manpower—did him in, more so than a difference between mareriel.
yes, but it wasn't just that. The war was already lost by that point, due to all of the other factors. Lee was being pointlessly stubborn drawing out the inevitable. And its not just a hindsight thing, they knew they were beaten long before.