And that source seems wrong when claiming sexual use is modern, since it absolutely is used in sexual contexts in Latin, e.g. in Augustine's Confessions.

How is it used, and are you referring to the original Latin, or a translation? Since seduction includes sexual seduction by virtue of its generality, he could have used the word to mean sexual seduction specifically. If the context is clear, you can omit the adjective. Given that Augustine does talk about his sexual decadence prior to his conversion, I can imagine him using the unqualified "seduce" to mean the specifically sexual, which would be apparent from context.