What level are we making here? I have never seen this phrase explained in non-vague terms. Dragon Quest is Square Enix's second most important franchise and its natural that third-party speculation will gravitate towards a company's flagships, it's completely fair to expect DQ after FF and unfair to think the only thing DQ has going for it in speculation are leaks.
Basically, while they could go for DQ, they could go for a SE thing that's more known worldwide too. They could simply go for another FF character if they think it'll sell better.
You also didn't read what people said about Erdrick then. Erdrick is only getting worldwide knowledge due to the leaks. DQ has some on its own merits. There's a huge difference in what is known worldwide. Erdrick needed a boost from leaks to even gather attention outside of a vocal minority of fans in the UK and US regions. We know he's hard to recognize outside of Japan.
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I'll just cover the other points a bit better than unnecessary quoting;
Joker is a worldwide known character. Persona 5 did wonderfully. DQ isn't actually doing super well on sales in the West even to this day, sadly so. Persona 5 getting a character can be attributed more to Sega or Sakurai looking outside of Sonic for stuff. In fact, what is the most noted franchise out of Sonic in Sega? Even the next top-seller? It's something people really don't know. This is why it's not exactly comparable to the DQ situation.
Likewise, no, we shouldn't outright expect DQ because FF was in. That's silly. We should acknowledge it as a legitimate Smash option. Expecting stuff leads to vast disappointment as you hype yourself up a bit too much. We could literally get no DQ content. And I honestly think DQ deserves to be in Smash(though I'd choose Slime easily as the rep, but that's just me).
Dragon Quest being popular in Japan doesn't mean anything outside of a good base roster choice. Smash will sell worldwide... base game. DLC does not inherently sell well in every part of the world. Using a worldwide character is the least risky move they can make. Whether it's a DQ character or another FF character. Sephiroth, for instance, would instantly sell easier than Erdrick, mainly because he's more known to a vast degree. But also because he's a worldwide gaming icon. Erdrick is not a worldwide icon. He's a Japanese icon. Slime is a worldwide icon. Luminary... I'm not sure if he could be called an icon, truthfully(though I'm not sure how to explain why his worldwide knowledge being higher exists, yet he might not be an icon. It'd probably just makes sense to say he's still an icon at this point).. Of course these factors can be ignored if they want to. But they're still important ones that shouldn't be brushed over. Look at businesses objectively, especially for DLC. You're telling me a character that only one region knows will sell well in all regions? Come on. That's just ridiculous. It's not a good argument that Erdrick will be a guaranteed seller. And the target of Smash as a whole is the entire world. We already know what the target is.
The actual point that never was brought up that favors Dragon Quest is Sakurai is most interested in celebrating Japanese gaming. This doesn't help Erdrick at all, but it does help DQ in itself. Sure, Sakurai being a huge fan of DQ3 is cool. He's also a huge fan of Geno, who isn't playable despite the fan demand. Recognition may be an actual factor here. Joker has it more than Geno, we can say that at least. Slime definitely has it over Erdrick.
Now to go over the flaw with the Brave stats here; it could work for Erdrick, or others. The fact we can't inherently make him the only possible one it could work with makes it flawed as any real evidence. Especially since it only points to one particular version of Erdrick(his chibi design), but we have no way of knowing that they'd use that one either. Any version could be pushed at this point. Have we even seen what version of Erdrick is pushed(I'd like to know) the most?