Meh, just a coincidence they guessed certain Hero alts. 8 has the popularity factor in the west, and I believe 3 and 4 are some of the most popular in Japan. 11 S was being worked on at the time too.
I'm gonna play devils advocate for a minute here. You can agree to disagree or entirely disagree with me, its okay.
1. Before this post, we had no credible leak actually mentioning Dragon Quest. All we had was Vergeben's 7 character list, and even that was fishy because all it named were the biggest SE characters anyway, yet nothing pointed to DQ being the character at the time. Tansut's leak came after this, and all he leaked was Erdrick. He consistently called him Erdrick then. The "Brave" codename leak happened in a January patch, nearly a month after this.
2. This post hard claims "HERO", and characters represented by literally those 4 games. I'd also argue that DQV, VI or VII are just as popular, if not more popular than DQ IV. We can retroactively confirm to ourselves that these 4 are definitely the most obvious, but I specifically remember people ONLY campaigning for Erdrick or Luminary, not really questioning the possibility of Solo (DQ IV) or Eight, while some people argued for others here and there. I think its important to remember this.
3. Bethesda has already let it slip that they talked to Nintendo about having a Smash rep. This is why the Doom Slayer bandwagon truly started. It quite literally is the only character/franchise Sakurai has ever mentioned by name from them. He has noted the franchise for being the father of FPS's. So while it makes sense for a fake leaker to add it for this reason, it actually helps this one, because.....
4. The leaker is 50/50 right now. They have been 50/50 from a post made back in December 2018. Just think about that for a minute. Before this, an overwhelming majority of people clamored for Steve and said Banjo was a pipe dream. I specifically remember having those conversations on this very forum. So before any credible leak came around, this person managed to tell us Banjo and Hero (with the possibility of him being represented by 4 games, all of which are now correct). So far, they have gotten nothing wrong.
5. Lastly....Monster Hunter. This has been an especially weird one. The representation its received is odd, especially because it has a boss to which no character actually stands at its opposite, 2 songs (which is surprisingly NOT generous of Capcom, even if its for a boss stage), and 1 spirit. Its a weird predicament. And IIRC, Monster Hunter had its own catagory of songs (Titled mh____) in the files rather than grouped with the "Other/Miscellaneous" category.
Take what you will from this. I think its legit. But if I had to safe guess things from here on out, it was always Doom Slayer for me, and Hunter always seemed like a possibility because of those circumstances (never something I'd guess though).
The only issue I have with this "leak" is the Monster Hunter. Regardless of what Reggie said at the Game Awards, the Monster Hunter franchise is already in Smash Ultimate. If Monster Hunter already has music and the Rathalos as a boss in the base game, why was the Monster Hunter himself (or herself) included? This is a minor point, but would adding the Hunter mean removing the two Monster Hunter tracks from the other franchises music list and putting them into the supposed Monster Hunter track list?
Thing is, you can take Reggie's comment to mean "unrepresented series" in terms of fighters. Aka, no Mario, Sonic, MGS, Zelda, etc etc etc. Monster Hunter has no representative on the fighter level, so it technically is unrepresented.