A popular complaint seen here and elsewhere about this game:
Why isn't there a Legendary (my favorite hero) card yet? or
If there is a UR/Leg card for (hero I think is over-rrated) then why is (hero I like more) only a Rare/SRare?
People want it all, and they want it now, but just because a particular member of the Marvel Universe isn't currently on a card, it doesn't mean they have no plans to add them in later. In fact, if everyone was already in game, fall-off would be happening at a more rapid pace and the game's shelf life would be much shorter. By adding in cards in smaller numbers during events, they have an opportunity to give us more to look forward to.
Some people don't like the idea that we already have so many Iron Man/Wolverine/Captain America/Hulk cards, but this too makes perfect sense. Casual players want their favorite heroes in their decks, at least to start. So by having these popular characters available at a variety of rarity levels, the opportunity is there to build decks with the heroes you like regardless of your maturity within the game. Given my previous point about wanting to be able to look forward to future additions, I'm also perfectly OK with additional cards of the popular heroes/villains at rarities they already exist at. I'd much rather chase a new SSR/UR Spider-man for my deck, than, say a new SSR/UR Puck (sorry to all the Alpha Flight fans)
So, until I get my Legendary [Forbush-Man] Irving Forbush+ card, I'll happily pursue the next DD/Elektra/Bullseye cards, or Spidey/Electro/Lizard, or even Thunderbird/Banshee/Sunfire/Krakoa... the possibilities remain endless.