Chrom is not an Ike echo because it makes no sense to make him an Ike echo. ALL echos we have seen have the same weight, speed, power, and range. Chrom shares none of this with Ike. Ike's weight, speed, power, and range are all attributed to him using a very heavy two handed sword. Chrom uses a one handed sword. It would make no sense for Chrom to be as powerful as Ike, as slow as Ike, as heavy as Ike, or have the same range as Ike. Chrom's Falchion is considerably shorter than Ike's Ragnel, and seeing as Lucina is using the exact same Falchion as Chrom there is no way Sakurai can justify changing its size.
Again every echo we have seen has had the same stats (Weight, Speed, Power, and Range) as the character they echo. Echo fighters are supposed to be easy additions, and no echo fighter we have seen has had those stats changed. Lucina only got her sword's attributes changed from Marth's, but they still share the same stats everywhere else with Marth being slightly taller. Chrom echoing Ike would be completely forced. I know Robin's Palutena guidance compares Chrom to Ike, but even Sakurai knew that making Chrom echo Ike would be pushing it. I saw Chrom as a Roy echo three miles away as it made much more sense. Roy is the middle ground between Marth and Ike, and fits Chrom well. I know people still think Roy and Marth are the same, but Roy has moves that Marth does not (about six or seven). In my opinion that more than justifies Roy getting his own echo.