My two cents: working through the Avengers chronologically, Mantis and Swordsman are the first and most significant gaps you encounter in "assembling" (I kill me) that display ... beyond them, we have some representation of every full-time member of the Easties until you get to Doctor Druid in 1987.
Yes, there are characters who need alternate looks (Hercules) and characters whose figures are hideously outdated (Hellcat), but we have some version of them.
Juanita is the biggest hole in a later, spin-off team's line-up (WCA), and Nikki isn't a fully-fledged member -- Nikki also builds out a team we only have two members of, rather than finishing/ near finishing a roster. To wit, most of the double-digit vote getters are characters who complete rosters or put us a single other character out from complete rosters: Armor, Valkyrie, Psylocke, Marrina, Hepzibah.
Thank you for coming to my TED talk. Next, why I still want Valkyrie more than Mantis.