There is a wide gulf between what most of the idiots that stormed the capitol believe and understand of the law, and what the NG will. That doesn't mean it will impede someone that's decided to go full jihad suicide bomber, but when you're a guy standing on the line with a gun, and you've got guys left, right, and behind you that also have guns, the calculus is a little different. Hasan killed a lot of people at Fort Hood, but he did it by being the only armed guy in the room. The NG guys aren't hard by any means, they are weekend warriors. Even if some are truly radicalized and decide to go out in a blaze of glory, they will still have a hard go of it. None of them will have any access to Biden or Kamala, even with a long gun. They will probably be forward facing outside the police line, and certainly outside the SS bubble. It wont stop them from indiscriminate spraying of the crowd, but there is little to no chance they even get a LOS to the seated audience. The SS is running the inauguration, not the capitol police.
Many in the MAGA crowd still truly believe they did nothing wrong, or that they wont face serious charges. The military has a different rule book, and like I said, if someone decides to pop off, its a suicide pact. I haven't seen anyone in MAGA show that mindset yet, the ones that stormed the capitol didn't do it guns drawn. Not dismissing their intentions, but a chickenshit in the crowd that pops off some rounds at a door is much different than a uniformed soldier turning on their oath, service members, and country.