I can't really agree... his main goal was to find a way to alleviate the shoulders of his family from having to purify the toxic mana.
But he was too slow for that. What if Simon's medicine would have killed the king aka Ark's father, it would have been too late. Or Julius wouldn’t even have been affected by mysterious drug if Ark would have stopped him from drinking it. I am judging him because his mental age, at 17, was actually 25 so he might would have been able to stop the rebellion ever happening.
The author implied in the early stages of the story that the MC's mind was regressing due to having been reincarnated in a 6-7 year old child. Maybe that is her excuse for how slow he was.
Don't get me wrong, I was as frustrated as you are now. The plot might have had a lot of flaws, but I just found it unfair that you summarized the MC's whole personality in keeping Julius interested in him. Since, ultimately, it was thanks to his efforts that the story had a HE.
I didn't really like the fact that Ark 's whole personality was to keep Julius interested in him. I mean he knew who instigators are, and still didn't do anything?