I would suggest that you haven't read Miller very closely. It is pretty clear that had anyone been present to represent Miller and give evidence that a short barreled shotgun was indeed a suitable militia weapon, the Court would have found that Miller had a right to possess it. The Court said that there was - no evidence before the Court - because Miller was dead and his lawyer didn't bother to show up.
At the time of Miller, yes, short barreled shotguns had been used by the military. Just not that short.
"the Court would have found that Miller had a right to possess it."
Mr. Miller was not arrested for possessing a short barreled shotgun. He was arrested for possessing a short barreled shotgun without a federal tax stamp.
You can argue all you want whether of not this was a suitable militia weapon. The fact is, it lacked a stamp. He violated the federal law that required one on this type of weapon.
Methinks the court used the “no evidence” line to neutralize the effect of Miller et al not showing up. They knew how important the case was, but couldn’t achieve a fair ruling without the defendant present. Saying
Actually when the oral arguments (or presentation might be a better term, since as you point out, there was no representation for Miller. Although it might be more accurate to say that Miller did not have a lawyer once the case was dismissed at the district court level. That of course would not be allowed today, one would be appointed, even if, as was the case, the individual could not be found). They did find Miller's body a few days before the SC issued it's opinion. He went down shooting, his .45 at his side, and it had been fired. I've never read if a killer was ever found, or even really looked for. The guy was a bootlegger and bank robber after all, he probably had lots of enemies, and few friends in the "peace officer" business.