Sengoku, Rayleigh, Katakuri, even Mihawk are all calm and calculating. When their hand is forced, they won’t back down nor fear anything just like Law. They’re not really headstrong characters like Luffy.
For Coby, he’s inexperienced and growing. This “conqueror material” is pretty much hoopla. The conquerors we have are all varying in personality. You just need really strong willpower, that’s why Usopp unlocking CoC is a real thing imo. The dude can show the strongest willpower at the right moment.
Coby will always be the clearest example that the whole “muh kingly qualities” thing is BS
You’re either born with it or you’re not
If not for Luffy beating Alvida and motivating him he would’ve been an East Blue Pirate’s slave for the rest of his life
But XYZ character can’t get it because they don’t possess the qualities
Oda has never had a rule regarding conqueror’s that he hasn’t broken. Conqueror’s are supposed to have an “unbreakable will” but Chinjao lost to Garp once and completely gave up
I’ve said it for ages and I’ll say it again. Oda will give conqueror’s to whoever he sees fit regardless of whether it makes sense or not
At this point, yeah it's arguable that a strict pattern is no longer a thing.
But let's be honest, Oda did really play into the "kingly qualities" thing multiple times. Played into "personalities" of conquerors etc.
There are many cases where this was blanantly stated in manga. Stuff like those guys aren't the type to work under others, would tend to squabble if put together, unreasonably stubborn, indominable spirits, etc.
Whitebeard used this line of thinking to deny Oden even.
It didn't help that the poster boys of conquerors - Roger, the OG Yonkos and the 4 new gen conquerors (Luffy/Ace/Zoro/Kid) perfectly fit the description as well. Unreasonably stubborn and prideful knuckleheads.
One can't fault readers who chose this interpretation really.
I think it's a mix of both. Oda wants to have his cake and eat it too (unsure if this is the correct analogy lol).
Oda wants to use the persona argument when he wants to (especially when he wants to do something like highlight the persona), but sometimes he just hands it out to whoever just cause he wants to (like Koby)