Sam, DY: Ah, but what happens when someone with that Mesorah claims that it is integral to Yiddishkeit and that you are missing something important without it?
and PAA, So if someone claims something as a mesorah is there any way to disqualify him/it?
For some reason, you both are not getting past framing this discussion in terms of and in the context of debating an issue and trying to prove someone wrong.
Whether your kashyas convince him or not depends on the strength of the kashyas and the strength of his convictions.
I’m making one point: a mesorah is not automatically wrong just because it’s not written. Obviously, though, it’s not automatically right either.