If you make laws regarding guns, only law abiding gun owners would adhere to them. Criminal won’t.
You can use this (non)logic in regards to any and all laws. Drunk driving is illegal, the majority of people follow the law. A few don’t. Does that mean you strike the law from the books? No
Robbing banks is illegal. The majority of people don’t rob banks. A few do. So, does that mean we removed the laws? No
Ban assault weapons, their manufacture, sale, and import. Require background checks, and close gunshow/online loopholes. If it takes you a few weeks to get your precious gun, fine as that required background checks will prevent someone with a history of mental illness or criminal background from purchasing one through legal channels.
Will a few that can’t buy them legally have to spend a horrendous amount of money to smuggle them in? Probably, but that doesn’t mean you don’t ban them! Same applies to high capacity magazines.
The idea of not passing sensible gun reform laws just because a few won’t obey is as ridiculous as making child pornography legal because a few won’t obey the laws against it.