This is absolutely wrong. He still wanted revenge. Why do you think he initiated the Black Rebellion? It wasn't to establish a new country based in Tokyo, it was to lure Cornelia so he could extract information about his mother's death from her and then kill her. (He only succeeded halfway there).
If anything, Euphie was interfering with his plans (see his reaction to her at the end of ep 21, where he practically was labeling her his enemy) so getting rid of her (however unplanned) in 22 was a key step in eventually launching the battles that would result in a utopia for Nunally (Tokyo) and revenge for his mother (defeating Cornelia, Shneizel, and the Emperor).
Later in R2, he still fights for his own goals and even abandons the Black Knights upon learning Nunally was governor (until Kallen dragged him back). And arguably everything he's doing now is to find out the truth while his army sits back and relaxes in its new haven in the CF.