I think I was wrong, at least as far as Fellay is concerned.
To be honest I won't pretend to be 100% sure who's right, but I see no meaningful sense in which what Bishop Fellay says differs from FSSP.
This isn't like some of the other stuff that's been mentioned, whether SSPX regularly talking to Rome, or obeying Rome's commands on the '62 missal or fasting rules or what have you. Fellay seems to straight up embrace hermeneutic of continuity here.
Which means he belongs in the FSSP.