gksu and kdesu are unsupported for >10 years iirc

I know.

they were not more secure than sudo

No, they were, barely, but they were, they were wrappers around sudo that provided "a more user-friendly and secure way to run graphical applications with elevated privileges, by handling environment variables and permissions better than using sudo directly."
They've been deprecated in favor of pkexec.
sux is wrapper around su which transfers your X credentials, it sucks, don't use it.

There's no difference between running it via sudo or pkexec, however polkit provide additional protections to prevent running unsafe apps with elevated privileges.

pkexec literally uses Polkit and PAM under the hood.

pkexec runs the program in a "minimal known and safe environment" to avoid potential security issues like code injection through environment variables. pkexec also sets the PKEXEC_UID environment variable to the user ID of the process invoking it, providing more information about the context. pkexec is more secure than using sudo -i for running graphical applications, as it can prevent certain types of privilege escalation attacks. This increased security is largely due to the use of PolicyKit (Polkit) with pkexec. Polkit is a framework that provides a way to define and enforce fine-grained access control policies for privileged operations. With Polkit, the system administrator can define rules that determine which users or processes are allowed to perform specific privileged actions, like running a GUI application as root. This provides more granular control compared to the blanket root access granted by sudo.

PAM and GVFS are not "privilege elevation frameworks" whatever you mean by this.

You're right, PAM is an authentication framework and GVFS is a whole other thing that leverages polkit and authentication agents. My bad.