I agree that the issue is a nuanced one. But I think the value of the point originally being made is that some have been inclined to view the Antonine dynasty as a regime that had a preconceived notion that it was better to adopt worthy heirs than to choose a son if available (not that this is what you think; I'm not attempting to strawman you). The reality is that Nerva, Trajan, Hadrian and Antoninus Pius did not have sons. Nerva adopted Trajan to avoid getting overthrown by the Praetorians and the general Nigrinus (based in Syria). Trajan, Hadrian and Antoninus adopted men from within the family rather than biological sons, whom they did not have. This isn't the same thing as what was seen in the Tetrarchic period, when in 293, 305, 308 and 311 biological sons failed to succeed their fathers.