That's also a fair point. I don't think there is a clear line. That is a problem, but it's one we can work with.
I think there will always be debate, and probably should be. The line will probably shift around a bit.
It gets additional complications in the US because it seems to be largely state controlled. That leads to inconsistency and other questionable regulation.
Some areas of the US are far more restrictive than Canada, and other areas are much less.
I think that for restrictions to be effective, it must be at a supply level. A gun should be acceptable every state, or none. Only law-abiding people are incapable of taking them across state lines. So what's the point restricting something in one state if they can just drive an hour and get one.
I don't see a better alternative. It's a very complicated issue.
You make fair points that I don't really disagree with, but where do you draw the line? California has enacted strict ammo control laws where you can't bring out of state purchased ammo and you need receipts to present (if necessary) to prove you purchased the ammo from a specific places and that you are limited on how much you can have. Do I need 500 rounds of ammo and 30 round clips for hunting? No. Will a slingshot protect me during a communist revolution? No.
I bought a crossbow a few months ago and customs opened the box to inspect and probably tag it because those are considered firearms in some counties here. I don't own a gun, but "less lethal" weapons are already regulated to shit and i can't even fire a crossbow at any archery range in my county.