That's why you create a lengthy random key (that you know it cant be brute forced) and encrypt everything using it and symmetric encryption.

Than you store that random key encrypted with asymmetric algorithm.

Shh, don't give them any ideas!

If you have read anything at all about encryption written since 1997 (probably before, that is when I first started reading) you already knew that.

If.

Most ransomware authors, I'd wager, have not been reading since before 1997.

gpg supports using public / private keypairs to encrypt any amount of data you like. I use it for uni-directional backups from machines where trust is an issue.

Or is the reality of this that it's just encrypting a symmetric key with the asymmetric cipher, and then encrypting data using that key?

Everything is encrypted with a symmetric key. It is just that sometimes there is an asymmetrically encrypted symmetric key packet included in the message so that GPG (or whatever) does not have to ask you for the symmetric key. This is all fairly generic, if you actually have the symmetric key you can use it directly even if a key packet exists. This means that you can give some entity a key to decrypt a particular message/file without revealing your asymmetric secret key associated with your identity.

Advanced ransomware use a hybrid scheme that generates a new symmetric key for each file and then encrypts that with an asymmetric key.