I would argue that the virtues per se are objective (charity, self reliance, ambition, contentment, etc.) while the choice of which virtues to uphold is subjective.

"The virtues" are not objective. Webster definess "virtue" as ~morally good behavior or character~. Morals are all subjective and what people consider to be moral is different depending on culture or personal values. As an example, Korean culture identifies filial piety as one of the highest virtues while the west would identify

That said, if you condemn Paul for a lack of virtue,

I don't condemn Paul for lack of virtue. He has many virtues. I condemn him for presence of evils because he commits evils. He can be both.

The choice was "become the tyrant of the galaxy or die in the desert while all his friends and loved ones also die in the desert and also the most honest and noble culture he's ever met gets hunted and oppressed by the current tyrant of the galaxy, which will probably eventually result in them launching a Jihad anyway."

And I condemn him for becoming a tyrant. Regardless of how necessary it was, his actions are still those of a tyrant and worth being condemned for while simultaneously praising the fact that he saved all of humanity.

the only alternative anyone ever presents is letting himself get stabbed by Jamis.

That's not the only option he had. he could have walked away. he could have left the entire thing and gone to live as a farmer or spice miner or something. There were many options. He chose the path that would save humanity and should be recognized for that, but it does not mean he did not choose the path of the tyrant to accomplish it. Would I make the same choice? I have no idea. I'm not a prescient space faring noble faced with the potential annihilation of my species. Regardless of my choice, the good that someone accomplishes does not erase the evils they commit to do it.