The handbook suggests that symmetric encryption is appropriate (and therefore not less secure than public key encryption?) when only you need to access the plaintext. But according to this post, since
gpg --symmetric only requires a passphrase, an attacker only needs to brute force this passphrase rather than the full 128/256 bit key generated from it.
It seems to me that the correct procedure then is to actually have a 128/256 bit key file which is used to symmetrically encrypt my data; which itself is symmetrically encrypted with a key generated from a passphrase, just like how private keys are protected. This would require an attacker to brute force the full symmetric key- even if they acquired my key file, they would still have to brute force my passphrase.
gpg support this sort of usage? Is my understanding of the situation flawed, is there a reason why this isn't a valid use case?
Or to put it another way:
In this question it is assumed that passphrase protection is sufficient- but basically my question is what if I don't trust myself to memorize a good 256 bit password? Can I use a symmetric key file just like with my private key? Obviously I could just actually use my private key, but the handbook suggests that the symmetric encryption would be the idiomatic choice in this situation.