AAQ – I’m referring to the probability of one’s being Jewish altogether, something ‘ujm’ ridiculously challenged. (Although technically חזקה is enough, like by almost everything else.) Any pre-Haskalah/mass assimilation maternal yichus is equal in this regard, whether you can trace your GGGM to Sanz, or Vilna, or Aleppo. (The latter probably being even better yichus.) The Gemara you refer to is concerned about the (albeit remote) possibility of other forms of פסולי יחוס.
To extend your logic, I think, good middos is the only sure sign of good yihus, and opposite – of opposite.
Absolutely correct, but it’s not MY logic, it’s a Gemara in Kiddushin 71a, which is brought להלכה למעשה in detail in Even HaEzer Siman 2. So, don’t be משתדך with trolls…