2FA is not going to save from both instances I mentioned above, its just a security layer to protect when someone manages to brute force our exchange wallet password from somewhere on the internet, even still 2FA can be bypassed if few ways even though its not that much easier.
2FA provide additional security, it is still protecting the wallet but some people make the mistake by having their wallet app and 2FA app on the same device, this is where the mistake is coming from. It is good to have the 2FA all on a different device so that it will be difficult for the wallet to be compromised.
If you're keeping your private keys safe there's a possibility of exchanges getting hacked so keep your Bitcoins on your own wallet.
Self custody is the best but some people prefer custodial means, if not your key it is not your coin. It will be good to make your post clearer next time, what you are trying to say is true.