Let's say my system has been pwned, and an attacker can see what text I am typing into my email client, as well as the decrypted text of received emails.
I have been using a GPG token to carry out all of the cryptographic functions (decrypting and signing). Theoretically, my secret GPG key should still be unavailable to an attacker, even though my system has been pwned, because the GPG token does not reveal my secret key to the system.
However, so what? If my system has been successfully attacked, and the attacker can see what an email reads after I have decrypted it, what is the point? Or, is it the case that an attacker will be able to read my decrypted emails if I've been using a GPG token on a pwned system?
If an attacker actually has the kind of access to your system you're describing -- "can see what text I am typing into my email client", then you're done. They would almost certainly also have access to arbitrary files, etc on your machine or any attached storage devices, including your pgp private key.