-I don't know about Isaac, but Geno is a fan fave everywhere.
-Shadow's popularity means nothing, if he truly is in, uit's because he's the most no brainer echo ever besides the also rumored Ken, so i doubt popularity was a factor in including Shadow.
-Rythm Heaven is a niche series in the west, besides chorus kids only get brought up for reasons you already listed
-Mach Rider has been on Sakurai's head since the days of melee, he said so in an interview.
So you have Banjo-Kazooie, the only character with undoubtable west bias, 2 Echos that are a no brainer, Geno, who is popular everywhere, 2 characters who have had smash buzz for years and Isaac.
again, i see no real west bias.