The Confederacy was doomed as soon as they fired on Ft Sumter, the only question was how long.
I agree the South lacked the resources to win a protracted war. Perhaps, however, the South could have won by using a different strategy or if the things had gone differently before Lincoln defeated McClellan.
The Buchanan Administration transferred most of the contents of Northern armories south before Lincoln took office. Winfield Scott's favoritism resulted in Southern officers being better trained--and holding higher positions--than those from the North. So at the beginning of the war the South actually had more material and a better officer corps.
As I see it there were some ways the South could have won.
The first was by invading the North after Bull Run. A successful invasion might have led the North to sue for peace. This was, of course, contrary to the will of Jefferson Davis, and IMHO was a huge mistake on his part. (It resulted, I think, from his belief that not invading the North was necessary to gain the support of England and France. Another major mistake by Davis and something that Lincoln made impossible by emancipating the slaves.)
The second--which the South tried--was by making the North grow war weary and abandon the struggle. This stratagem almost worked. Had McClellan defeated Lincoln the South would have gained its independence. But Northern victories shortly before the election--especially those of Sherman--thwarted that hope.
Also, had Lincoln been assassinated before his second election things might have been different. As I see it, much of the resolve that kept the North in the war came directly from Lincoln.
As I see it, the South came closer to winning than is usually thought. Had it not been for Northern victories--which in some ways were nearly miraculous--just before the election McClellan would have beat Lincoln resulting in the South gaining its independence. (Had Davis not replaced Johnson with Hood the whole outcome of the war might have been different.)