Professor Ibrahim answered both points that there was actually no consensus on either matter. He concludes that consensus cannot abrogate authentic text.
I agree with his conclusion, but I don't quite see his rationale. What if there was consensus on the two matters cited? Would that have made a difference?
At more than one level, I agree that consensus cannot abrogate text, so I am addressing only the logic in the OP rather than the conclusion.
1. It seems to me that the above examples would be used to argue "can Sahaba rulings abrogate text?" because in both examples, it was Sahaba (Khalifa and other Sahaba) that made the ruling. I believe that this what Professor Ibrahim is referring to, just making the point that the examples do not show evidence of consensus.
2. Trying to prove that X can abrogate Y by showing that in some instance
X was used to overrule Y is fundamentally flawed. It is a purely 'precedent' argument and precedent in and of itself is not a proof of validity.
3. I believe that in the case of consensus, people are implicitly invoking the hadeeth to the effect that a unanimous conclusion of the nation cannot be wrong, so they are deriving the authority from that hadeeth, not from the precedent. The simplest argument against this line of reasoning is that there is no unanimity that any text was abrogated, period, notwithstanding what is used to abrogate it, so the hadeeth about unanimity does not apply to any abrogation claim.