You're overestimating the value of laws. Laws don't create civilization, the civilization creates laws. The jungle is always there, we just generally avoid it because going to the jungle means our survival is down to just our abilities and judgement. It's far preferable to stay in civilization where we have our best chance of survival.
Your hypothetical examples all depend on people being weak willed in the face of a constitutional crisis. If people are weak, there being a King or not a King makes no difference. The US has no King, but people are weak towards Trump, and it's the same result as your hypotheticals, just different titles.
And why would the King risk his cushy life to do any of these things? Why would someone who is in a position like that for the rest of his life risk it all for some short term gain?
So corruption can happen in a republican, and it seems to me it's more obvious when someone doesn't give royal ascent, and it's very unlikely a King who has guaranteed housing in a palace for life being waited on hand and foot would risk that for a small bump in his stock portfolio. It seems you're imagining the King behaving like a corrupt politician, but you're not explaining how replacing the King with an actual politician makes that less likely to happen? If anything a term limited politician is more likely to do any of these hypotheticals, get that money in the limited time they're in the position to get it. And the people that voted for that politician are more likely to look the other way than if a King started doing shenanigans.
