I normally like Source Gaming's stuff, but man, their argument against multiple reps as alts is extremely weak.
"It would be weird to have one pack of the Fighter's Pass have more value than the rest of the pass."
This already happened multiple times in the last pass. Joker and Terry had more spirit battles than the other packs, Hero had more unique alts than everyone else, and Terry had more music than literally everyone else combined. It's pretty clear Sakurai isn't going to limit the content in each pass to ensure equality.
"Unlike the Heroes, the ARMS characters have unique identities and abilities. Combining them is like putting Ryu, Akuma, Sakura, and Dan into the same slot."
Woo boy. A lot to unpack here, and all of it is wrong.
First off, the Heroes do have unique abilities in their source material that aren't translated to Smash. Eight lost the ability to use spears and boomerangs, Solo lost his knives, bows, and axes, Erdrick lost his whips, and Eleven lost his two-handed greatswords. Likewise, they gained previously only usable by one other hero (Eight is the only one of the heroes to use Psyche Up in Dragon Quest) and were never usable by any of them (no Dragon Quest hero can use the Woosh series of spells in game). What makes these characters work within a single moveset is their lowest common denominator: they all use swords, shields, and some of the same magic. As such, losing some abilities and gaining others isn't a huge deal, because their general outline is consistent with their most primary abilities in Dragon Quest.
Similarly, Spring Man, Ribbon Girl, Ninjara, and Min Min also have a lowest common denominator: relatively balanced stats, a similar build, and punching/grabbing with long stretchy arms. These are the key elements that make these four unique relative to other characters in both inside and outside of ARMS. As such, these characters feel like themselves when they display these abilities. Do these four have unique attributes from each other they could capitalize on in a Smash appearance? Of course, but these are tertiary abilities that could realistically be sacrificed or distributed to all four to flesh out their moveset, similar to the unique aspects of the heroes.
The shotos, by comparison, are a bad example because they don't have this common denominator. While they all share the hadoken, shoryuken, and tatsumaki, the way these abilities function are drastically different. Akuma has dark hadokens that he can fire in the air, Sakura has shorter hadokens that she can charge and send at an angle, and Dan has weak hadokens that are fired with one hand. The Dragon Quest heroes, by comparison, use a similar style of swordplay and have a good number of overlapping spells (the frizz family, the zap family, the snooze family, the heal family, etc). The ARMS characters are in a similar boat. They mostly throw standards jabs that they can then curve to hit opponents. Assuming they're using the same family of ARMS, Spring Man punching someone is not that different from Ribbon Girl punching someone.
TL;DR: The Heroes are unique but have a common abilities that let them share a spot. This is similar to Spring Man, Ribbon Girl, Ninjara, and Min Min, but not the Shotos.