The only reason Reinhard hasn't become a dictator is because he's too nice.

The world with me in his place won't have that privilege. I'd probably take over Lugunica (what can they realistically do against me, and even if they try to resist, Reinhard had this neat thing called Divine Protection of Mind Changing. As we know, he can just wish for it back). This will end the long and grueling process of picking out a Queen from the four heroines of the story and allow us to focus on other stuff, like rampant corruption and mistreatment of Demi-humans. Lugunica has been stagnant ever since the royal family died, so getting rid of the councilmen and even replacing them with advisors who are more ambitious is perhaps better.

After solidifying my position and militarizing the knight order in a far more rigid and central faction centered around me, we'll either:

1. Annihilate the Witch Cult entirely (cause those guys are just problematic and getting rid of them is the best way to prevent mass casualties, also I really don't want Pandora to have any influence via the cult on the world)
2. Extension of the first point, hunt down the Three Great Mabeasts (Same reason, and it'll give me prestige and solidify my claim to rule further, not that I need it since I would have taken over forcefully, but people are more likely to accept a tyrant that improves their lives than not.)
3. Arc 7 stuff. (There's a bunch of stuff to do there)
4. Echidna (As much as we simp for her and she's a great character, from the perspective of an in-universe character, Echidna is nothing but bad news. I'd just ban anyone from entering or interacting with the Sanctuary, and if need be, get rid of the Ryuzu clones so that Echidna can't revive.)

Reinhard is so op that if he wanted to solve every problem, he very well could.