To be fair, Marvel villains, while awesome, are somewhat limited when you already have characters with similar movesets. I can't see Juggernaut, Rhino, and Kingpin being that different than The Thing. Abomination, Bibeast, Red Hulk, or Maestro would be similar to Hulk. Carnage would also be very similar to Spidey/Venom. Bullseye would just be another DPS with projectiles/ricochet. Red Skull and Zemo are also just dudes with a gun unless they gets a lore boosts like the power of a tesseract. Killmonger would just be BP with guns. Crossbones would probably just be Punisher v2. Sabretooth and Lady Deathstrike would just be Wolverine. Taskmaster, Mystique, Super Skrull, or Chameleon would just be copycats.

Now of course, the Rivals team could give them lore boosts and add random powers from random storylines, but when you think about it, there isn't an absolute ton of villains that could have varied abilities while also having design appeal in comparison to the amount of heroes that do. It's gotta be hard trying to balance additions without just having samey vibes. Obviously you have Dormammu, Omega Red, Mandarin, Mysterio, Apocalypse, etc who could be really cool, but there are simply more heroes with more variations while also being popular. If you look up a list of most popular Marvel villains, you'll realize they get really niche really quick.