More information from people who are smarter than me:
https://www.reddit.com/r/hardware/comments/izmi1k/ampere_poscapmlcc_counts/g6k2h0a?utm_source=share&utm_medium=web2x&context=3
https://www.reddit.com/r/hardware/comments/j09yj5/poscap_vs_mlcc_what_you_need_to_know/?utm_source=share&utm_medium=web2x&context=3
tl;dr: POSCAPS not worse or cheaper than MLCC; the fault lay primality with Nvidia for not allowing them to test configurations with the correct drivers, and less so on the AIBs.