While everything you say is true, we generally fail to see the technological advances that happened in other decades, including the decades we've lived through, or maybe that's a given. Of course, the thing about the 1860s was there was a war going on, same as the 1940s, when there were a few (very few) Civil War veterans still living. In fact, my wife has some photos of veterans parading in Alexandria, Virginia, wearing their old uniforms. Some were on horses. I think the photos were taken in the 1920s, perhaps earlier.
It is interesting that you mention how there were a lot of inventors in Washington (and Richmond, too, no doubt) trying to get the right people interested in their wares. Yet at the same time, it is always remarkable how difficult it has always been, and still is, to get a new weapon accepted, sometimes even more difficult than it is to get it manufactured and adopted. Usually it takes the dedication of a few men during wartime to prove the worth, if not always the practicality, of some newfangled gun or other weapon. Even so, often as not the improvement is only marginal of what was already out there, at least in some cases. Take field artillery, for instance.
Rifled field artillery was around in time for the Civil War. We might wonder 150 years later why smoothbores were still used, given all the advantages of the rifles. They shot farther, were more accurate and hit harder. All well and good, only a smoothbore of the same weight on the ground shot a bigger projectile and could do more damage against advancing troops. But if you couldn't get as many of either kind as you could use, it was a moot point.
Surprisingly, automatic weapons (small arms) have always been a hard sell right down to the present day. You only have to read this forum to see that not everyone believes in the value of automatic fire. They were either seen as too expensive, too "thirsty" (used a lot of ammunition, wasting it or not), unreliable in some cases and apparently justifiably so, and so on. In 1914 a British infantry battalion only had two machine guns and the Lewis Gun was in the future. By 1940 that had changed, of course.
Would the outcome of the war have been changed? Doubtful. It doesn't follow that one side would have had the new technology and not the other, although the South had a disadvantage in manufacturing. That didn't keep them from building ironclad gunboats, submarines and even some artillery. They may have had Lee but they didn't have Grant.
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.