Kurt really has some.... stubbornness to his character.. If it wasn't for that, maybe he could have been a better personality and could've kept his title as the landlord, but purely because of his stubbornness he'll lose it to Well
Its not stubbornness its pride. How would u feel if uve be getting told all ur life that ur gonna be the next lord, being groomed every moment and only being educated in kingcraft, then ur littlest brother comes along with magic, slays a dragon, n all of a sudden everybody says HE should inherit, meanin ur whole life was a LIE!?
Its the same with Vegeta. As Crown Prince he is told all his life that hes the best, then some commoner who was supposed to be the weakest even among fellow Saiyin commoners beats him, then kills Freiza who hes spent his life plotting to kill himself, after becoming the legendary Super Saiyin, rumored to be the strongest of them all.
Kurt holding grudge and envy Well is understanable. I'm the older brother in my family and we have the things call pride. I think I can safely says that many older brother in a family has that pride as a older brother. But trust me Kurt won't be this way or stubborn if he didn't get overwhelm or being lead around by other corrupt people by the nose.