The problem is that the Buddha made it quite clear that mindfulness of breathing was not simply samatha but instead a fully capable vehicle for insight. To refer to the breath as "conceptual" or to claim that knowing the character of the breath is somehow not insight or not capable of leading to insight is to ignore literally hundreds of statements to the contrary in exchange for a few later commentarial designations that were invented long after the Buddha passed on. There is no way one can read the suttas and truly come to the understanding that anapanasati is "purely samatha."
Gain and loss, status and disgrace,
censure and praise, pleasure and pain:
these conditions among human beings are inconstant,
impermanent, subject to change.
Knowing this, the wise person, mindful,
ponders these changing conditions.
Desirable things don’t charm the mind,
undesirable ones bring no resistance.
His welcoming and rebelling are scattered,
gone to their end,
do not exist.
- Lokavipatti Sutta