I don’t think you can prove papal successions historically speaking beyond the early 9th or 10th century, the historical record for that is simply lost although you can prove the Catholic Church existed very early on (St. Ignacius - 110AD) which was writing to the congregation in Smyrna, the same referenced around the same time by Paul and John of Patmos.
I agree with most of your claims although you must clarify what would make for a JW signature teaching in its own historic record. We all know the cross, trinity and other staple Christian teachings were commonly discussed by writers in the first Zion’s Watch Tower and its predecessor publications which JWs claim were their start, yes they eventually rejected those, but they didn’t come out of the gate with them. Russell clearly states that Jesus should be worshipped, not doing so would have made him a heretic in both the Millerite and Presbyterian movements, Presbyterians believe in the Catholic Church although they believe the Roman Catholic Church was corrupted. Although we know the Russelite movement went through its own schisms, only one branch resolving into WTBTS/JW, JW themselves would not admit to the true establishment being by Rutherford after another schism.
So in short, what is the signature teaching of JWs that would be taught by Russell and accepted by modern JW - because there are not many if any teachings that currently overlap and have remained constant.