Logically you can't expect a single guy who already got his initial plan out first to instead focusing on the the patreon request.
He need to push out his story on duke before adding in extra option which you can harm or jail the duke at the negative consequences, like duke have 4 retainers at his side, so if you jail him, that should be some opposition from duke faction to try suppress you and rescue duke.
If you kill duke, your other neutral retainers and duke faction will out to get you first, because it is a tyranny by CK3 standard. Causing rebellion, so you need sizable armies to fight civil war. So you need to weed them duke faction first so you can grant your royal guard into marquis role to fill in the power gap. So many option.
The Duke is the first forgin event, and the game mechanics treat it like a tutorial for making choices in Forgin policy. That is until the game rug pulls your choice.
CK3? I assume you mean Crusader Kings 3? Frist of all CK mechanics are an approximation of feudal society not 100% accurate, which means other games that have different mechanics like an RPG maker game would be more historiclly accurate by not doing what CK3 does. CK3 doesn't have Nobles rebelling for stupid pervy reasons. This game establishes nothing about a "Duke faction", all he should have is his knights under his duchy. You think they want to fight so the Duke can perv? CK3 doesn't have a scenarios like this. The game establishes nothing that would legitimate the Dukes rebellion, or that he has a faction beyond his own personal knights. The Queen's other lords should be opportunistic and lining up to take his position for such stupidity.
Removing a rebellious noble is not Cusing tyranny without extra contexts. If he rebeled because the Queen wanted a ridiculous tax rate from him and the other lords. Sure tyranny is a good metric. If the Queen was supposed to offer protection from bandits or forginers, and the crown was too weak to help, and she imprison him or his family when the Queen failed in her duty. Then yes causing tyranny would be a good Metric.
The Duke has no allies, only subordinates. Even if the Duke did have allies what is he going to promis them? All he wants is to perv on the queen... what are his allies getting in return for RISKING TREASON???!!!!
If you don't go along with the Duke he immediately and unapologetically starts scheming rebellion. He is a rebellious treasonous vassle, and your reputation would be hurt way more by not severly punishing him. As for Tyrrany.... what is Tyrranical or unreasonable about the Queen wanting the Duke to simply do his duty during a time of war during a barbarian invasion? Earning Tyranny points implies the Queen was unreasonable at any point in the professional relationship.
Your Hypothetical "The Duke can rebel because lords in real life did it from time to time" excuse doesn't take into account that a real life lord would have a demand like Marriage or some other big ticket item for his whole faction. If the Duke wanted a marriage to get an advantage over the Queens other lords, then withholding some support could make some sence. But it also Wouldn't be done during an invasion by an enemy power like the barbarians. Would be counter offered with larger demands for the whole "Duke faction"... Even in the event of an actual treasonous rebellion In real life once the Queen won the consequences would be obvious and swift. His head would be place on a spike and he would be drawn and quartered. With his body parts sent to different regions to set an example of him.
This argument is so flawed.
Pro duke argument:
Lords in real life withheld support and rebeled for reasons that made sence in the power politics of the time.
Therefore the Duke can do it for the flimsiest stupidest reasons at the worst possible time considering the barbarian threat and the Queen wrong for doing something about it and teaching him the fuck around and find out lesson of life. SMH.