As the saying goes, comparing people leads to death, comparing goods leads to rejection.
While both are monarchs, at least the King of France was willing to stand and fall with his throne, proving to the Orleans Party of France that they had not followed the wrong person.
But as for the Tsar...
The contrast between Tsar Nicholas I and Louis Philippe is so stark that Arthur feels that even if someone like the Great Dumas, who had personal animosity and severe political differences with Louis Philippe, were to evaluate them, the Frenchman who always valued chivalry wouldn't claim Nicholas I was superior to Louis Philippe.
After all, the biggest reason the Great Dumas and Arthur could reconcile was because Arthur insisted on staying at the forefront during the London riots, not abandoning his subordinate officers at Scotland Yard, even taking a bullet for it.
