The whole point of a brain wallet is store nothing on any device.
Agree
If that's the only advantage, it's a pretty small one compared to the inherent decrease in security.
Can you really not afford the storage space of a 100 kilobyte wallet file?
Don't understand why you go on about affording storage space, it is not about that.
It's about storing the 'private key/password' in your own memory, your brain. The name says it all: brain wallet.