Nothing is impossible, it's just that currently there is no way you can rate someone like Rashford anywhere near Mbappé. Of course anything can happen within the next few years, Mbappé can disappear into irrelevancy like Pato, Quaresma, Gourcuff or countless other great talents. Currently, I'd have those tiers of forwards that are quite similar in terms of talent:
Tier 1: Mbappé
Tier 2: Dembélé/Sané/Sterling/Sancho/Vinicius (with the latter two actually having played too few games to assess, and Sterling having the "lowest" ceiling but being the most consistent player out of the bunch)
Tier 3: Rashford/Martial/Coman/(Asensio) (with Martial being probably the most talented, but most inconsistent)
Tier 4: Baily/Brandt/Jesus and the rest