Something important to remember; moveset potential is always sweet. But it doesn't mean it's easy to implement. Likewise, being unique for the sake of unique is pretty hard to implement too. Shortcuts are taken for a reason, via clones, semi-clones, echoes, or using someone as a base. Wolf borders on semi-clone, but is vastly unique otherwise. Whereas Ness used Mario as a base, but is still highly unique(with you could argue only a slightly similar B move and a few A moves with some similar hitboxes, perhaps. At least in Smash 64).
How one can be unique isn't enough in itself. How you can balance that out into a character that flows well is vastly more important. Erdrick doesn't lack this one bit either. He has tons of ways to play in a balanced manner that works well. Just adding the extra weapons shouldn't be your goal alone. It should be if you can make the moveset coherent while doing that. Is party members the best way to do things outside of a Final Smash? You have to consider loading times. We don't have a lot of characters who can summon stuff due to the game lagging. So sometimes you have to look past potential and look more for feasible first.
Both sides have a point, basically. Nothing wrong with wanting 100% unique characters. It's just not feasible in any fighting game, if you want a cast larger than... 30 perhaps would be the right number. Likewise, there's nothing wrong with clones/semi-clones/echoes/similar move-using characters either. They're both valid and successful styles. Likewise, Smash runs on character choices. The more there is, the more fanbases it pleases. So less characters is not optimal anymore. You could argue they're going overboard, but it's still working as a design pretttttty well.
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Now, for me, Erdrick is someone who I always found workable as a fun and unique character. I never really got the idea that somehow holding a sword makes you similar to another user. Same franchise or otherwise. It's not that simple. The closest similarity you could at best say is the same hitboxes, but other than disjoints, there's tons of animations from non-weapon users that would be effectively the same thing. So it's really a matter of how to use his items and spells that heavily represent Dragon Quest yet still be feasible. I always felt magical attacks could work well, but being a sword with magic doesn't seem like it fits how DQ works super well bar a few special items you can get. Thus, I'd say something closer to Robin or Ganondorf to a degree. Erdrick could use some spells for moves, and his sword for others. Another thing I'd like to see is referencing how the Hero Class has multiple armors. So basically Leather, Steel, Magic, Armor of Erdrick(though I wouldn't mind the actual character be the Hero Class with multiple alts. It'd honestly feel the same overall thing as I want the Hero Class more than any specific Hero. That's what I grew up, so it means the most to me). My thoughts are something similar to this, though it's definitely not a fully refined idea;
-Leather Armor: Least amount of weight, so he moves the fastest, but also is easier to knockback.
-Steel Armor: Is harder to knockback by a bit, but also slightly slows down in return.
-Magic Armor: Gets even heavier, and moves far slower than the Leather Armor, but also heals a slight amount of Percent as you move.
-Armor of Erdrick: The strongest armor, with the most weight. Now you take no damage from Poison itself(moves that technically have Poison, like Ivysaur's, are normal damage, you're just immune to the status), and have a little bit of Super Armor as well.
I got no clue how to have to Swords work. I also don't remember them nearly as well for the first game. Just the Flame Sword and Sword of Erdrick at best.