The fig lead that they will use to justify this distinction was hinted at in Seila Law, another case when they allowed the firing of members of independent agencies: they will say that the Federal Reserve has a "long tradition of independence" that distinguishes it from newer agencies, even though they are all operated under the same law.
If that distinction sounds preposterous to you, then congratulations, you reached the same conclusion that Justice Jackson reached when she complained that the conservative majority is playing "Calvinball" to reach results-based decisions regardless of statute, precedent, and the Constitution.
For those who didn't grow up in the 90s, Calvinball is a reference to a fictional sport from the comic strip Calvin and Hobbes, in which the sport's rules are made up and change constantly.