Yup, that sounds like a perfectly sound political strategy. Destroy all the commoners. Can't see any possible negative repercussions from that.
I know feudal societies aren't too terribly advanced politically, but you would imagine that during the life he led after he was (probably) adopted to a related noble house, he would have learned that commoners are the necessary cornerstones of wealth for landlords and other gentry, and without them, nothing actually functions. Like, I don't expect a political treatise out of these works, but a little more reasonable motivation than, "Commoners are evil because they killed my dad and so I should kill all of them" would be nice.
Petty reasons like pride work better for that, because as awful as they are, they are at least emotionally logical. "I don't want any peasants in my social class because I'm better than them and I'll undercut every opportunity they have to change the status quo to keep it that way" makes more sense than literally destroying the base upon which the feudal system, and therefore the characters own position and status, are built upon. An even better idea for the cause of the rift could be a Jacobin-inspired insurrection in a neighboring country, which could result in much more heightened tension and fear between nobles and commoners, which can be developed in a number of useful ways. In particular, the nobles would have a valid reason to fear commoners as a class in that case, sharing stories of the equivalent of the Terrors, even if the individual commoner they are speaking to hasn't displayed any revolutionary tendencies. As it is, there was a failed revolution, the nobles apparently stomped the rebels, but continue to be fearful jackholes who are bent on making sure the peasantry rises up again.
The way the noble/commoner conflict has been portrayed so far has been disappointing. Like most incarnations of this trope, it takes the lazy approach of simply assuming the commoners are the good guys and the audience will by default sympathize with them (for multiple reasons; they are the viewpoint characters; they are usually explicitly confirmed to be; the nobles are immediately and nearly universally portrayed as brutal monsters; a sense of democratic equality unsuited to the time period on the part of the readers; etc) with very little argument made as to the causes of this conflict or any possible solutions other than... well, murder of all the nobles. Which kinda proves their point, non?