Nah, let Valt be flustered and cute. It goes well with the sudden change of character when he snaps. Also, ig the fact he changed race and apparences can be freeing in some ways. Yeah, he wants to rule the world blablabla, it doesn’t mean he likes what comes with being an evil king.
Actually, I wonder why tf he wants to rule the world. I doubt he wants to kill everyone and make despair reign given his little speech the "time passes, with each death and each birth. A world worth ruling" part (quote not accurate, lazey in chp1.4 pg5).
tl;dr: Valt is so cute I forget he can crush my skull like a paintball. Leave him be.