Z,
I agree that we need to define who is a legit rav.
Maybe like that: if rav x is legit, and he respects rav y, then rav y is legit. Maybe exclude some outliers of rabbis who love humanity so much that they’ll respect anyone, and cases when someone changed dramatically over time.
You can easily get a chain from Satmar rebbe to r Schachter: thru Moshe and r Soloveitchik. There might be hard cases but this is not one of them.