This is nonsense.

A single OpenBSD kernel on bare metal can do whatever it pleases.

A Linux kernel on Xen HVM could, due to this bug, do slightly more than it ought to have been able to do.

(In this sense, the LLDT bug was worse.)

Every kernel (not named seL4) has vulnerabilities. The question is not whether OpenBSD would have been vulnerable to this specific issue, but whether Xen generally has fewer bugs than the OpenBSD kernel - or, for that matter, the Linux kernel, since the grandparent mentioned a bunch of Linux sandboxing technologies.

edit: To be absolutely clear, per the grandparent, I'm assuming an environment where unrelated people are running software on the same hardware, either using their own kernel under Xen or user processes under jails.

I'll take the world where we have the odd hypervisor vulnerability over the world where we have to increase power output by multiple orders of magnitudes and pave the planet with datacentres to run every service as a single-instance, non-virtualised server.

I guess Theo prefers runaway global warming to the odd data breach. Which makes him the idiot, to use his own language.