If one's "faith" is incomplete or corrupted, then it's not the real Faith. The protestants have corrupted/incomplete faith; and they are heretics.
I don't think anyone could argue that Abraham and Moses didn't have the real faith, however the articles of the faith of the authentic judaic religion were clearly incomplete compared to those of Catholicism.
By definition, they must have had an implicit faith in the articles of the faith that they were ignorant of.
On the other hand, protestantism and other false religions are not merely incomplete. If anyone tries to follow their teachings seriously, they will end up committing countless mortal sins against the natural law and they will certainly go to hell.
False religions are both incomplete and corrupt.