Sorry. Should be:
I’m not seeing disagreement on this point or on the question of whether those IN Purgatory are bound for Heaven.
Baptism of the dead by proxy is what is being discussed in that passage, sorry for any confusion. The practice implies that the salvation of the dead can be affected by the actions of the living, ie: that there is a second chance, and so citing that passage in support of purgatory implies the same, that the disposition of those presumably held in that state or place is not certain.