Yes, I know how Kerberos works. The TGT is not bound to anything though, it can be stolen and reused elsewhere. And in the default setting, an attacker doesn't need to rely on Kerberos as an authentication mechanism, since NTLMv2 support is widely available. It's available by default.
Nevertheless, did GP mean Kerberos tickets by "domain credentials"? How does Kerberos prevent the use of password managers? I'm confused.