My opinion on Smash's DLC business-wise is:
"****'s overpriced, yo."
But Nintendo knows we'll buy it, they know I'll buy it, and they're not really going to stop.
Nintendo could make "Playable Sandbag DLC" and even if he literally did nothing, you know that thing's going to sell more than most indie titles.
Otherwise, additional effort begets additional payment. It's simply a fact of life, and unless they resort to something terribly cancerous like Overwatch style lootboxes or locking them behind single-entry sequels like pre-Street Fighter V, this is probably the best business model (excluding the price-tag) that Nintendo could go for in terms of additional DLC (other than metaphorically burning cash and giving us free stuff for the sake of giving us free stuff)
(Now, if I personally was asked to come up with a compromise, I'd implement a fully fleshed out and functional training mode playable with other people. Then, everyone would get the DLC characters, but only for that training mode. Payment unlocks them for regular use and online. That way, everyone can at the very least learn the matchup and how to fight against them, while also playing them and seeing what their strengths and weaknesses are, but not in any real combat.
So online, you won't be blindsided by a character you couldn't experience unless you paid extra money, but you also won't be just handed a free character at the expense of the other business practices I described above.)