Who's the most iconic/biggest/deserving Pokemon? Most deserving Fire Emblem character? I'm making a list of all the All Stars that could be added. So far, it's Inkling, Octoling, Dixie Kong, RIdley, Rayman, Toad, Paper Mario, Spring Man, Bandana Dee, Impa, Wolf, Ice Climbers, Tom Nook, Isabelle from Animal Crossing, and Minecraft Steve.
The issue with Pokémon is that the most iconic are all first generation Pokémon, going by name recognition. Guys like the Kanto starters, Meowth, Eevee, Magikarp, Gyarados, Ditto and so forth. But that's also not really how Pokémon get into Smash. Folks like the Alola starters, Mimikyu, and maybe the Ultra Beasts would be more fitting in Smash at this point in time. My personal pick is Decidueye.
Fire Emblem is similar in that regard. The series is much more niche than Pokémon as well, but generally Smash sticks to main lord characters. So in that regard, folks like Chrom, Alm, Celica, Lyn, Hector, Eliwood, Eirika, Ephraim, Micaiah, Sigurd, Seliph, and Leif, as well as Alfonse and Sharena for Heroes, are all of equal importance to the ones we have within their own games. Certain lords in particular have high popularity within the Fire Emblem fanbase, namely those with international releases for obvious reasons. Of them I believe Celica has the best case for getting into Smash.
But just in general, the notion that a character is "deserving" is kind of a nothing statement. At the end of the day, only Sakurai can be an unbiased judge of that since he decides the roster, so saying any current character is undeserving is kind of fallacious. I'd advise against using it as an inclusion criterion.