Not trying to sound like I'm against Erdrick, but what legs does the characters have the stand on besides leakers? People assume he's basically in because of leakers, but those are not official and aren't 100% reliable so let's remove those from the equation for a moment.
In the speculative process, you can't ignore leakers when they were the reason Erdrick became considered in the first place. It started all the way back when Vergeben was saying a Square Enix character was being considered. Fast forward to the seven Square Enix character candidates (Crono, Geno, Sora, Sephiroth, Erdrick, Luminary, and Slime), and now the stage is set.
So let's throw things we know at the wall now that we have this list. Brave is literally Erdrick's class. He is called Yuusha in Japan, which translate to Brave or Hero. The evidence for this translating to Brave is that one Kirby photo in which the Japanese Nintendo employee literally called it "Brave's shield." While Sora has a "brave form" (valor form) and many other characters can be considered a brave person, Erdrick is the closest character who fits the adjective/title because he is literally classified as Brave. Stats can change easily and height stat can very well mean jack in the grand scheme of things.
Now why Erdrick over the other characters in that seven Square Enix list? Dragon Quest is a cult icon in Japan and efforts are being made to make it more popular in the west with Nintendo's collaboration. You've probably heard the story over literal muggings over the series happening in 1980s Japan because people wanted Dragon Quest 3 that badly. There is also a dedicated museum exhibit for Dragon Quest. Dragon Quest influenced games like Final Fantasy, Shin Megami Tensei, Pokemon, even the ****ing Streetpass feature for the 3DS. Nintendo has shown in the February direct that more Dragon Quest news is coming, so it's clearly a relevant series.
Ignoring leaks, you will also have to ignore the one 5chan leak (the one that only claims Joker and Erdrick) that said Persona 5 Arena is getting delayed for a Granblue fighting game, which Polar Panda confirmed. This one leak that predicted this specific detail said that Joker and Erdrick are in. Remember, this is the 5chan leak that is not predicting all five DLC characters, but just Erdrick and Joker. Interestingly, it also predicted more overseas Dragon Quest marketing, which Nintendo seems game on doing right now this year.
I can also use Tansut, who has that source that predicted Cloud, and that same source is saying Erdrick. He came out that he was requested to hold off from sharing Cloud until near his reveal. However, since Erdrick was practically an open secret around December, it's fine to share him early.
I'm gonna link you to
Teeb147
and her
megapost from the Erdrick support thread because it nicely compiles the evidence, sources, and links, and then explains what needs to be said with said facts.
It's not just individual pieces of evidence that's used to justify Erdrick. It's how they collectively fit together.