Well, I'm glad the father realized he is a dumbass for not training his heir for the one freaking job he has. And it's not like Ars wasn't mature enough for it. Sure he is kind and peaceful, as part of being a reincarnated modern person, but he was also very mature for his age. If anything, he should have been following his father on the nastier aspects of ruling from an earlier age.
Also, kind of pointless of him to ask them to follow Ars. "Remember the guy who actually recruited you, saw your true value when no one else did? Yeah, please pretend like my opinion matters and follow him as a favor to me, even though I'm talking shit about how he is so weak." I would get it if they were his own retainers that he recruited, and he was asking them to show his son the same loyalty they showed him, but these guys are Ars own retainers. They're only technically his because he is the lord and thus the one actually paying their salaries. The whole scene is him saying "do what you were already going to do, but pretend I mattered at least a little in this comic." Like seriously, has the father done anything of note? Did he ever even start to prepare Ars for his role?