It is that complexity associated with BOD that proves the error. Trent spoke clearly insofar as the laver of regeneration or the desire for it were immediately contextualized by the reference to John 3:5, yet the BOD advocates will ignore this context to push their error. Or, as you've indicated, they will emphasize some opinion of two Church Fathers (Ss. Ambrose and Augustine) that could be construed in favor of BOD while ignoring 99% of the other Fathers who explicitly taught the necessity of water baptism.