What's the point of the crown?
All of what you said is true. There’s literally no reason for it.
The entire quest chain was nonsensical. I guess it wasted a little time and a few silver. Maybe it existed to handwave away why Rytlock was only trying to do this now? But they already did that via the research angle, and it’s not like he couldn’t have hunted down the pieces before.
It would have potentially made more sense if they tied the Iron Marches events to the last instance. If you recall the Priory team with the injured dolyak, they sent a runner on with some artifact. Say, completing the open world tasks leads to an instance where you arrive too late to save the runner, but you recover the artifact from mordrem. That artifact happens to be the crown, which you hold on to until you can figure out what to do with it. When you talk to Rytlock about the meeting, he is initially not optimistic. Then he recognizes the crown (thanks to his research) and only then concocts the plan to cleanse the Foefire.
My guess is that it was primarily added for lore reasons, to explain why it has taken so incredibly long to figure out a way to even attempt to end the Foefire.
Rytlock with Priory assistance would have had to have figured it out long ago without the added “wrinkle” of the crown which was apparently lost centuries ago and virtually unknown, much less all the other Charr who have no doubt tried as well (even Smodur says he’s been looking into it). The swords seem pretty “common knowledge” at least to the Priory and others knowledgable about the Foefire, but apparently not the crown.