I think it's much ado about nothing, basically. Richmond, as the south's second city (behind New Orleans) and center of industry, would have been a vital target for the Union and a locus of Confederate defense in any case. The Confederacy would quite literally have been incapable of maintaining their armies without the Tredegar Iron Works (cannons and iron plate, among other things), Richmond Depot (largest clothing and shoe factory in the south), and Richmond Armory (the Confederacy's only real small arms factory). Tucking the capitol away in Montgomery would not have changed that. If anything, it would have the disadvantage of removing the commander-in-chief and the war department from the most important theater of war, complicating the Confederate war effort at least to a degree. And, given Union incursions into north Alabama as early as 1862, you could make the case that the Confederate capital would have been more endangered and not less if it had stayed in Montgomery.

To take a wider view, because of geography and other factors, the Confederacy had a better chance of defeating the Union in Virginia than anywhere else. The Appalachians and the numerous west-east rivers constrained Union advances and ensured the Confederacy could concentrate their limited forces to meet them. Out west, the geography worked against the Confederacy. The front was vastly larger, meaning the defense would always be weak in some place, and the three great rivers - Mississippi, Tennessee, and Cumberland - functioned as vast highways for Union forces to travel down. Good historians are supposed to hate the idea of inevitability, but I have a hard time imagining how the Confederacy could have won out west. If there was to be a victory, it had to be won in Virginia.