I saw it already, but those hardware security features also secure the features you mention there. The other features were developed with the hardware security features in mind. Again, without secure hardware, it's possible for your software to be modified and no longer secure. That's the broken security model I keep mentioning.

While it could definitely be more secure than other ROMs, security was never tested without the hardware features and thus it could also expose you to attacks because of that. Worse, it could make you assume that you're secure when you're really not.

An excellent example is Cerberos. GrapheneOS is able to completely block attacks from Cerberos by disabling the USB port data lanes entirely, something that most (if not all non Pixel phones) are unable to do. Cerberos uses many zero day vectors to break in though the data lanes, and in this case you likely would not be able to block the attack. They'd be able to dump your phone contents and then much of the software security features wouldn't matter.